diff --git a/.changeset/avatar-button-sizing.md b/.changeset/avatar-button-sizing.md
new file mode 100644
index 00000000000..60ea3bfff0a
--- /dev/null
+++ b/.changeset/avatar-button-sizing.md
@@ -0,0 +1,5 @@
+---
+"@primer/react": patch
+---
+
+Avatar: Add min-width and flex-shrink protection to prevent unexpected shrinking in Button leadingVisual and flex layouts (#7974).
diff --git a/packages/react/src/Avatar/Avatar.module.css b/packages/react/src/Avatar/Avatar.module.css
index fc67531b9a7..25c9d6b62d1 100644
--- a/packages/react/src/Avatar/Avatar.module.css
+++ b/packages/react/src/Avatar/Avatar.module.css
@@ -1,7 +1,9 @@
 :where(.Avatar) {
   display: inline-block;
   width: var(--avatarSize-regular);
+  min-width: var(--avatarSize-regular);
   height: var(--avatarSize-regular);
+  flex-shrink: 0;
   overflow: hidden; /* Ensure page layout in Firefox should images fail to load */
   /* stylelint-disable-next-line primer/typography */
   line-height: 1;
@@ -18,16 +20,19 @@
   &:where([data-responsive]) {
     @media screen and (--viewportRange-narrow) {
       width: var(--avatarSize-narrow);
+      min-width: var(--avatarSize-narrow);
       height: var(--avatarSize-narrow);
     }
 
     @media screen and (--viewportRange-regular) {
       width: var(--avatarSize-regular);
+      min-width: var(--avatarSize-regular);
       height: var(--avatarSize-regular);
     }
 
     @media screen and (--viewportRange-wide) {
       width: var(--avatarSize-wide);
+      min-width: var(--avatarSize-wide);
       height: var(--avatarSize-wide);
     }
   }
diff --git a/packages/react/src/Button/__tests__/Button.test.tsx b/packages/react/src/Button/__tests__/Button.test.tsx
index e95eb5d614d..5abeecb98df 100644
--- a/packages/react/src/Button/__tests__/Button.test.tsx
+++ b/packages/react/src/Button/__tests__/Button.test.tsx
@@ -4,6 +4,7 @@ import {render, fireEvent} from '@testing-library/react'
 import {describe, it, expect, vi} from 'vitest'
 import React from 'react'
 import {IconButton, Button, LinkButton} from '../../Button'
+import Avatar from '../../Avatar'
 import classes from '../ButtonBase.module.css'
 import {implementsClassName} from '../../utils/testing'
 import {FeatureFlags} from '../../FeatureFlags'
@@ -708,4 +709,17 @@ describe('data-component attributes', () => {
         .toBeInTheDocument()
     })
   })
+
+  it('renders Avatar in leadingVisual without collapsing dimensions (#7974)', async () => {
+    render(
+      <Button leadingVisual={() => <Avatar src="primer.png" size={20} data-testid="button-avatar" />}>
+        Profile
+      </Button>,
+    )
+    const avatar = page.getByTestId('button-avatar')
+    await expect.element(avatar).toBeInTheDocument()
+    await expect.element(avatar).toHaveAttribute('data-component', 'Avatar')
+    await expect.element(avatar).toHaveAttribute('width', '20')
+    await expect.element(avatar).toHaveAttribute('height', '20')
+  })
 })