diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
index bc48bfd3dc7..a55fd0d3956 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
@@ -534,12 +534,9 @@ export default createRule<Options, MessageId>({
         }
       }
       const typeName = getTypeName(checker, propertyType);
-      return !!(
-        (typeName === 'string' &&
-          checker.getIndexInfoOfType(objType, ts.IndexKind.String)) ||
-        (typeName === 'number' &&
-          checker.getIndexInfoOfType(objType, ts.IndexKind.Number))
-      );
+      return !!checker
+        .getIndexInfosOfType(objType)
+        .find(info => getTypeName(checker, info.keyType) === typeName);
     }
 
     // Checks whether a member expression is nullable or not regardless of it's previous node.
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
index b72eb4f13c1..8c891aea624 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
@@ -509,6 +509,149 @@ declare const key: Key;
 
 foo?.[key]?.trim();
     `,
+    // https://github.com/typescript-eslint/typescript-eslint/issues/7700
+    `
+type BrandedKey = string & { __brand: string };
+type Foo = { [key: BrandedKey]: string } | null;
+declare const foo: Foo;
+const key = '1' as BrandedKey;
+foo?.[key]?.trim();
+    `,
+    `
+type BrandedKey<S extends string> = S & { __brand: string };
+type Foo = { [key: string]: string; foo: 'foo'; bar: 'bar' } | null;
+type Key = BrandedKey<'bar'> | BrandedKey<'foo'>;
+declare const foo: Foo;
+declare const key: Key;
+foo?.[key].trim();
+    `,
+    `
+type BrandedKey = string & { __brand: string };
+interface Outer {
+  inner?: {
+    [key: BrandedKey]: string | undefined;
+  };
+}
+function Foo(outer: Outer, key: BrandedKey): number | undefined {
+  return outer.inner?.[key]?.charCodeAt(0);
+}
+    `,
+    `
+interface Outer {
+  inner?: {
+    [key: string & { __brand: string }]: string | undefined;
+    bar: 'bar';
+  };
+}
+type Foo = 'foo' & { __brand: string };
+function Foo(outer: Outer, key: Foo): number | undefined {
+  return outer.inner?.[key]?.charCodeAt(0);
+}
+    `,
+    `
+type BrandedKey<S extends string> = S & { __brand: string };
+type Foo = { [key: string]: string; foo: 'foo'; bar: 'bar' } | null;
+type Key = BrandedKey<'bar'> | BrandedKey<'foo'> | BrandedKey<'baz'>;
+declare const foo: Foo;
+declare const key: Key;
+foo?.[key]?.trim();
+    `,
+    {
+      code: `
+type BrandedKey = string & { __brand: string };
+type Foo = { [key: BrandedKey]: string } | null;
+declare const foo: Foo;
+const key = '1' as BrandedKey;
+foo?.[key]?.trim();
+      `,
+      parserOptions: {
+        EXPERIMENTAL_useProjectService: false,
+        tsconfigRootDir: getFixturesRootDir(),
+        project: './tsconfig.noUncheckedIndexedAccess.json',
+      },
+      dependencyConstraints: {
+        typescript: '4.1',
+      },
+    },
+    {
+      code: `
+type BrandedKey<S extends string> = S & { __brand: string };
+type Foo = { [key: string]: string; foo: 'foo'; bar: 'bar' } | null;
+type Key = BrandedKey<'bar'> | BrandedKey<'foo'>;
+declare const foo: Foo;
+declare const key: Key;
+foo?.[key].trim();
+      `,
+      parserOptions: {
+        EXPERIMENTAL_useProjectService: false,
+        tsconfigRootDir: getFixturesRootDir(),
+        project: './tsconfig.noUncheckedIndexedAccess.json',
+      },
+      dependencyConstraints: {
+        typescript: '4.1',
+      },
+    },
+    {
+      code: `
+type BrandedKey = string & { __brand: string };
+interface Outer {
+  inner?: {
+    [key: BrandedKey]: string | undefined;
+  };
+}
+function Foo(outer: Outer, key: BrandedKey): number | undefined {
+  return outer.inner?.[key]?.charCodeAt(0);
+}
+      `,
+      parserOptions: {
+        EXPERIMENTAL_useProjectService: false,
+        tsconfigRootDir: getFixturesRootDir(),
+        project: './tsconfig.noUncheckedIndexedAccess.json',
+      },
+      dependencyConstraints: {
+        typescript: '4.1',
+      },
+    },
+    {
+      code: `
+interface Outer {
+  inner?: {
+    [key: string & { __brand: string }]: string | undefined;
+    bar: 'bar';
+  };
+}
+type Foo = 'foo' & { __brand: string };
+function Foo(outer: Outer, key: Foo): number | undefined {
+  return outer.inner?.[key]?.charCodeAt(0);
+}
+      `,
+      parserOptions: {
+        EXPERIMENTAL_useProjectService: false,
+        tsconfigRootDir: getFixturesRootDir(),
+        project: './tsconfig.noUncheckedIndexedAccess.json',
+      },
+      dependencyConstraints: {
+        typescript: '4.1',
+      },
+    },
+    {
+      code: `
+type BrandedKey<S extends string> = S & { __brand: string };
+type Foo = { [key: string]: string; foo: 'foo'; bar: 'bar' } | null;
+type Key = BrandedKey<'bar'> | BrandedKey<'foo'> | BrandedKey<'baz'>;
+declare const foo: Foo;
+declare const key: Key;
+foo?.[key]?.trim();
+      `,
+      parserOptions: {
+        EXPERIMENTAL_useProjectService: false,
+        tsconfigRootDir: getFixturesRootDir(),
+        project: './tsconfig.noUncheckedIndexedAccess.json',
+      },
+      dependencyConstraints: {
+        typescript: '4.1',
+      },
+    },
     `
 let latencies: number[][] = [];