diff --git a/app/javascript/images/donation_successful.png b/app/javascript/images/donation_successful.png
new file mode 100644
index 00000000000..ad10f9db7fd
Binary files /dev/null and b/app/javascript/images/donation_successful.png differ
diff --git a/app/javascript/mastodon/features/donate/api.ts b/app/javascript/mastodon/features/donate/api.ts
index 7a721a17daf..4ed80e843ff 100644
--- a/app/javascript/mastodon/features/donate/api.ts
+++ b/app/javascript/mastodon/features/donate/api.ts
@@ -58,6 +58,12 @@ export interface DonateServerResponse {
   default_currency: string;
 }
 
+export interface DonateCheckoutArgs {
+  frequency: DonationFrequency;
+  amount: number;
+  currency: string;
+}
+
 type DonateAmount = Record<string, number[]>;
 
 async function fetchCampaign(
diff --git a/app/javascript/mastodon/features/donate/donate_modal.scss b/app/javascript/mastodon/features/donate/donate_modal.scss
index 4be265c2fdc..d64a42520da 100644
--- a/app/javascript/mastodon/features/donate/donate_modal.scss
+++ b/app/javascript/mastodon/features/donate/donate_modal.scss
@@ -31,6 +31,11 @@
       display: flex;
       align-items: center;
       padding: 0.5rem;
+
+      &:hover,
+      &:focus {
+        background-color: var(--button-hover-color);
+      }
     }
 
     input {
@@ -52,12 +57,17 @@
     flex-grow: 1;
   }
 
-  .button.toggle:not(.active) {
-    background-color: inherit;
-    border: 2px solid var(--button-color);
-    color: var(--button-color);
+  .toggle {
+    border: 2px solid transparent;
 
-    &:hover {
+    &:not(.active) {
+      background-color: inherit;
+      border-color: var(--button-color);
+      color: var(--button-color);
+    }
+
+    &:hover,
+    &:focus {
       border-color: var(--button-hover-color);
       background-color: var(--button-hover-color);
       color: white;
@@ -66,11 +76,11 @@
 
   .submit {
     padding: 0.6rem 1rem;
+  }
 
-    svg {
-      fill: currentColor;
-      height: 1em;
-    }
+  button > svg {
+    fill: currentColor;
+    height: 1em;
   }
 
   .footer {
@@ -78,4 +88,18 @@
     color: var(--input-placeholder-color);
     font-size: 0.9em;
   }
+
+  .success {
+    .illustration {
+      max-width: 350px;
+      margin: 0 auto 1rem;
+    }
+
+    h2 {
+      font-size: 16px;
+      line-height: 24px;
+      font-weight: 500;
+      letter-spacing: 0.15px;
+    }
+  }
 }
diff --git a/app/javascript/mastodon/features/donate/donate_modal.tsx b/app/javascript/mastodon/features/donate/donate_modal.tsx
index ad98a660b3e..b6a4751e212 100644
--- a/app/javascript/mastodon/features/donate/donate_modal.tsx
+++ b/app/javascript/mastodon/features/donate/donate_modal.tsx
@@ -1,22 +1,20 @@
-import type { FC, SyntheticEvent } from 'react';
-import { forwardRef, useCallback, useMemo, useState } from 'react';
+import type { FC } from 'react';
+import { forwardRef, useCallback, useEffect, useState } from 'react';
 
-import { defineMessages, FormattedMessage, useIntl } from 'react-intl';
+import { defineMessages, useIntl } from 'react-intl';
 
 import classNames from 'classnames';
 
-import type { ButtonProps } from '@/mastodon/components/button';
-import { Button } from '@/mastodon/components/button';
-import { Dropdown } from '@/mastodon/components/dropdown';
-import type { SelectItem } from '@/mastodon/components/dropdown_selector';
 import { IconButton } from '@/mastodon/components/icon_button';
 import { LoadingIndicator } from '@/mastodon/components/loading_indicator';
 import CloseIcon from '@/material-icons/400-24px/close.svg?react';
-import ExternalLinkIcon from '@/material-icons/400-24px/open_in_new.svg?react';
+
+import type { DonateCheckoutArgs } from './api';
+import { useDonateApi } from './api';
+import { DonateForm } from './form';
+import { DonateSuccess } from './success';
 
 import './donate_modal.scss';
-import type { DonateServerResponse, DonationFrequency } from './api';
-import { useDonateApi } from './api';
 
 interface DonateModalProps {
   onClose: () => void;
@@ -24,23 +22,59 @@ interface DonateModalProps {
 
 const messages = defineMessages({
   close: { id: 'lightbox.close', defaultMessage: 'Close' },
-  one_time: { id: 'donate.frequency.one_time', defaultMessage: 'Just once' },
-  monthly: { id: 'donate.frequency.monthly', defaultMessage: 'Monthly' },
-  yearly: { id: 'donate.frequency.yearly', defaultMessage: 'Yearly' },
 });
 
+// TODO: Use environment variable
+const CHECKOUT_URL = 'http://localhost:3001/donate/checkout';
+
 // eslint-disable-next-line @typescript-eslint/no-unused-vars -- React throws a warning if not set.
 const DonateModal: FC<DonateModalProps> = forwardRef(({ onClose }, ref) => {
   const intl = useIntl();
 
-  const donationData = useDonateApi();
+  const donationData = useDonateApi() ?? undefined;
+
+  const [donateUrl, setDonateUrl] = useState<null | string>(null);
+  const handleCheckout = useCallback(
+    ({ frequency, amount, currency }: DonateCheckoutArgs) => {
+      const params = new URLSearchParams({
+        frequency,
+        amount: amount.toString(),
+        currency,
+        source: window.location.origin,
+      });
+      setState('checkout');
+
+      const url = `${CHECKOUT_URL}?${params.toString()}`;
+      setDonateUrl(url);
+      try {
+        window.open(url);
+      } catch (err) {
+        console.warn('Error opening checkout window:', err);
+      }
+    },
+    [],
+  );
+
+  // Check response from opened page
+  const [state, setState] = useState<'start' | 'checkout' | 'success'>('start');
+  useEffect(() => {
+    const handler = (event: MessageEvent) => {
+      if (event.data === 'payment_success' && state === 'checkout') {
+        setState('success');
+      }
+    };
+    window.addEventListener('message', handler);
+    return () => {
+      window.removeEventListener('message', handler);
+    };
+  }, [state]);
 
   return (
     <div className='modal-root__modal dialog-modal donate_modal'>
       <div className='dialog-modal__content'>
         <header className='row'>
           <span className='dialog-modal__header__title title'>
-            {donationData?.donation_message}
+            {state === 'start' && donationData?.donation_message}
           </span>
           <IconButton
             className='dialog-modal__header__close'
@@ -50,140 +84,44 @@ const DonateModal: FC<DonateModalProps> = forwardRef(({ onClose }, ref) => {
             onClick={onClose}
           />
         </header>
-        <form
+        <div
           className={classNames('dialog-modal__content__form', {
-            loading: !donationData,
+            initial: state === 'start',
+            checkout: state === 'checkout',
+            success: state === 'success',
           })}
         >
-          {!donationData ? (
-            <LoadingIndicator />
-          ) : (
-            <DonateForm data={donationData} />
+          {state === 'start' &&
+            (donationData ? (
+              <DonateForm data={donationData} onSubmit={handleCheckout} />
+            ) : (
+              <LoadingIndicator />
+            ))}
+          {state === 'checkout' && (
+            <p>
+              Your session is opened in another tab.
+              {donateUrl && (
+                <>
+                  {' '}
+                  If you don&apos;t see it,
+                  {/* eslint-disable-next-line react/jsx-no-target-blank -- We want access to the opener in order to detect success. */}
+                  <a href={donateUrl} target='_blank'>
+                    click here
+                  </a>
+                  .
+                </>
+              )}
+            </p>
           )}
-        </form>
+          {state === 'success' && donationData && (
+            <DonateSuccess data={donationData} onClose={onClose} />
+          )}
+        </div>
       </div>
     </div>
   );
 });
 DonateModal.displayName = 'DonateModal';
 
-const DonateForm: FC<{ data: DonateServerResponse }> = ({ data }) => {
-  const intl = useIntl();
-
-  const [frequency, setFrequency] = useState<DonationFrequency>('one_time');
-  const handleFrequencyToggle = useCallback((value: DonationFrequency) => {
-    return () => {
-      setFrequency(value);
-    };
-  }, []);
-
-  const [currency, setCurrency] = useState<string>(data.default_currency);
-  const currencyOptions: SelectItem[] = useMemo(
-    () =>
-      Object.keys(data.amounts.one_time).map((code) => ({
-        value: code,
-        text: code,
-      })),
-    [data.amounts],
-  );
-
-  const [amount, setAmount] = useState(
-    () => data.amounts[frequency][data.default_currency]?.[0] ?? 1000,
-  );
-  const handleAmountChange = useCallback((event: SyntheticEvent) => {
-    let newAmount = 1;
-    if (event.target instanceof HTMLButtonElement) {
-      newAmount = Number.parseInt(event.target.value);
-    } else if (event.target instanceof HTMLInputElement) {
-      newAmount = event.target.valueAsNumber * 100;
-    }
-    setAmount(newAmount);
-  }, []);
-  const amountOptions: SelectItem[] = useMemo(() => {
-    const formatter = new Intl.NumberFormat('en', {
-      style: 'currency',
-      currency,
-      maximumFractionDigits: 0,
-    });
-    return Object.values(data.amounts[frequency][currency] ?? {}).map(
-      (value) => ({
-        value: value.toString(),
-        text: formatter.format(value / 100),
-      }),
-    );
-  }, [currency, data.amounts, frequency]);
-
-  return (
-    <>
-      <div className='row'>
-        {(Object.keys(data.amounts) as DonationFrequency[]).map((freq) => (
-          <ToggleButton
-            key={freq}
-            active={frequency === freq}
-            onClick={handleFrequencyToggle(freq)}
-            text={intl.formatMessage(messages[freq])}
-          />
-        ))}
-      </div>
-
-      <div className='row row--select'>
-        <Dropdown
-          items={currencyOptions}
-          current={currency}
-          classPrefix='donate_modal'
-          onChange={setCurrency}
-        />
-        <input
-          type='number'
-          min='1'
-          step='0.01'
-          value={(amount / 100).toFixed(2)}
-          onChange={handleAmountChange}
-        />
-      </div>
-
-      <div className='row'>
-        {amountOptions.map((option) => (
-          <ToggleButton
-            key={option.value}
-            onClick={handleAmountChange}
-            active={amount === Number.parseInt(option.value)}
-            value={option.value}
-            text={option.text}
-          />
-        ))}
-      </div>
-
-      <Button className='submit' block type='submit'>
-        <FormattedMessage
-          id='donate.continue'
-          defaultMessage='Continue to payment'
-        />
-        <ExternalLinkIcon />
-      </Button>
-
-      <p className='footer'>
-        <FormattedMessage
-          id='donate.redirect_notice'
-          defaultMessage='You will be redirected to joinmastodon.org for secure payment'
-        />
-      </p>
-    </>
-  );
-};
-
-const ToggleButton: FC<ButtonProps & { active: boolean }> = ({
-  active,
-  ...props
-}) => {
-  return (
-    <Button
-      block
-      {...props}
-      className={classNames('toggle', props.className, { active })}
-    />
-  );
-};
-
 // eslint-disable-next-line import/no-default-export -- modal_root expects a default export.
 export default DonateModal;
diff --git a/app/javascript/mastodon/features/donate/form.tsx b/app/javascript/mastodon/features/donate/form.tsx
new file mode 100644
index 00000000000..99243b22ba2
--- /dev/null
+++ b/app/javascript/mastodon/features/donate/form.tsx
@@ -0,0 +1,154 @@
+import type { FC, SyntheticEvent } from 'react';
+import { useCallback, useMemo, useState } from 'react';
+
+import { defineMessages, FormattedMessage, useIntl } from 'react-intl';
+
+import classNames from 'classnames';
+
+import type { ButtonProps } from '@/mastodon/components/button';
+import { Button } from '@/mastodon/components/button';
+import { Dropdown } from '@/mastodon/components/dropdown';
+import type { SelectItem } from '@/mastodon/components/dropdown_selector';
+import ExternalLinkIcon from '@/material-icons/400-24px/open_in_new.svg?react';
+
+import type {
+  DonateCheckoutArgs,
+  DonateServerResponse,
+  DonationFrequency,
+} from './api';
+
+const messages = defineMessages({
+  one_time: { id: 'donate.frequency.one_time', defaultMessage: 'Just once' },
+  monthly: { id: 'donate.frequency.monthly', defaultMessage: 'Monthly' },
+  yearly: { id: 'donate.frequency.yearly', defaultMessage: 'Yearly' },
+});
+
+interface DonateFormProps {
+  data?: DonateServerResponse;
+  onSubmit: (args: DonateCheckoutArgs) => void;
+}
+
+export const DonateForm: FC<Required<DonateFormProps>> = ({
+  data,
+  onSubmit,
+}) => {
+  const intl = useIntl();
+
+  const [frequency, setFrequency] = useState<DonationFrequency>('one_time');
+  const handleFrequencyToggle = useCallback((value: DonationFrequency) => {
+    return () => {
+      setFrequency(value);
+    };
+  }, []);
+
+  const [currency, setCurrency] = useState<string>(data.default_currency);
+  const currencyOptions: SelectItem[] = useMemo(
+    () =>
+      Object.keys(data.amounts.one_time).map((code) => ({
+        value: code,
+        text: code,
+      })),
+    [data.amounts],
+  );
+
+  const [amount, setAmount] = useState(
+    () => data.amounts[frequency][data.default_currency]?.[0] ?? 1000,
+  );
+  const handleAmountChange = useCallback((event: SyntheticEvent) => {
+    let newAmount = 1;
+    if (event.target instanceof HTMLButtonElement) {
+      newAmount = Number.parseInt(event.target.value);
+    } else if (event.target instanceof HTMLInputElement) {
+      newAmount = event.target.valueAsNumber * 100;
+    }
+    setAmount(newAmount);
+  }, []);
+  const amountOptions: SelectItem[] = useMemo(() => {
+    const formatter = new Intl.NumberFormat('en', {
+      style: 'currency',
+      currency,
+      maximumFractionDigits: 0,
+    });
+    return Object.values(data.amounts[frequency][currency] ?? {}).map(
+      (value) => ({
+        value: value.toString(),
+        text: formatter.format(value / 100),
+      }),
+    );
+  }, [currency, data.amounts, frequency]);
+
+  const handleSubmit = useCallback(() => {
+    onSubmit({ frequency, amount, currency });
+  }, [amount, currency, frequency, onSubmit]);
+
+  return (
+    <>
+      <div className='row'>
+        {(Object.keys(data.amounts) as DonationFrequency[]).map((freq) => (
+          <ToggleButton
+            key={freq}
+            active={frequency === freq}
+            onClick={handleFrequencyToggle(freq)}
+            text={intl.formatMessage(messages[freq])}
+          />
+        ))}
+      </div>
+
+      <div className='row row--select'>
+        <Dropdown
+          items={currencyOptions}
+          current={currency}
+          classPrefix='donate_modal'
+          onChange={setCurrency}
+        />
+        <input
+          type='number'
+          min='1'
+          step='0.01'
+          value={(amount / 100).toFixed(2)}
+          onChange={handleAmountChange}
+        />
+      </div>
+
+      <div className='row'>
+        {amountOptions.map((option) => (
+          <ToggleButton
+            key={option.value}
+            onClick={handleAmountChange}
+            active={amount === Number.parseInt(option.value)}
+            value={option.value}
+            text={option.text}
+          />
+        ))}
+      </div>
+
+      <Button className='submit' onClick={handleSubmit} block>
+        <FormattedMessage
+          id='donate.continue'
+          defaultMessage='Continue to payment'
+        />
+        <ExternalLinkIcon />
+      </Button>
+
+      <p className='footer'>
+        <FormattedMessage
+          id='donate.redirect_notice'
+          defaultMessage='You will be redirected to joinmastodon.org for secure payment'
+        />
+      </p>
+    </>
+  );
+};
+
+const ToggleButton: FC<ButtonProps & { active: boolean }> = ({
+  active,
+  ...props
+}) => {
+  return (
+    <Button
+      block
+      {...props}
+      className={classNames('toggle', props.className, { active })}
+    />
+  );
+};
diff --git a/app/javascript/mastodon/features/donate/success.tsx b/app/javascript/mastodon/features/donate/success.tsx
new file mode 100644
index 00000000000..5c128ce7cad
--- /dev/null
+++ b/app/javascript/mastodon/features/donate/success.tsx
@@ -0,0 +1,70 @@
+import { useCallback } from 'react';
+import type { FC } from 'react';
+
+import { FormattedMessage } from 'react-intl';
+
+import donateIllustration from '@/images/donation_successful.png';
+import { focusCompose, resetCompose } from '@/mastodon/actions/compose';
+import { Button } from '@/mastodon/components/button';
+import { useAppDispatch, useAppSelector } from '@/mastodon/store';
+import ShareIcon from '@/material-icons/400-24px/share.svg?react';
+
+import type { DonateServerResponse } from './api';
+
+interface DonateSuccessProps {
+  data: DonateServerResponse;
+  onClose: () => void;
+}
+
+export const DonateSuccess: FC<DonateSuccessProps> = ({ data, onClose }) => {
+  const hasComposerContent = useAppSelector(
+    (state) => !!state.compose.get('text'),
+  );
+  const dispatch = useAppDispatch();
+  const handleShare = useCallback(() => {
+    const shareText = data.donation_success_post;
+    dispatch(resetCompose());
+    dispatch(focusCompose(shareText));
+    onClose();
+  }, [data.donation_success_post, dispatch, onClose]);
+
+  return (
+    <>
+      <img
+        src={donateIllustration}
+        alt=''
+        role='presentation'
+        className='illustration'
+      />
+      <FormattedMessage
+        id='donate.success.title'
+        defaultMessage='Thanks for your donation!'
+        tagName='h2'
+      />
+      <FormattedMessage
+        id='donate.success.subtitle'
+        defaultMessage='You should receive an email confirming your donation soon.'
+        tagName='p'
+      />
+
+      <Button block onClick={handleShare}>
+        <ShareIcon />
+        <FormattedMessage
+          id='donate.success.share'
+          defaultMessage='Spread the word'
+        />
+      </Button>
+      <Button secondary block onClick={onClose}>
+        <FormattedMessage id='lightbox.close' defaultMessage='Close' />
+      </Button>
+      {hasComposerContent && (
+        <p className='footer'>
+          <FormattedMessage
+            id='donate.success.footer'
+            defaultMessage='Sharing will overwrite your current post draft.'
+          />
+        </p>
+      )}
+    </>
+  );
+};