@@ -4,6 +4,7 @@
 
 ### Bug Fixes
 
+-   `TimePicker`: Fix date parsing for years below 1000 by implementing ISO 8601 compliant year formatting with zero-padding ([#75343](https://github.com/WordPress/gutenberg/pull/75343)).
 -   `Text`: Remove `text-wrap: balance` fallback. Only `text-wrap: pretty` is now used ([#75089](https://github.com/WordPress/gutenberg/pull/75089)).
 -   `RangeControl`: support forced-colors mode ([#75165](https://github.com/WordPress/gutenberg/pull/75165)).
 -   `ToggleControl`: Prevent `__nextHasNoMarginBottom` from logging a console warning ([#75296](https://github.com/WordPress/gutenberg/pull/75296)).
 
@@ -591,4 +591,46 @@ describe( 'TimePicker', () => {
 			} );
 		} );
 	} );
+
+	describe( 'ISO 8601 compliance', () => {
+		it( 'should handle years below 1000 with zero-padded output', async () => {
+			const user = userEvent.setup();
+			const onChangeSpy = jest.fn();
+
+			render(
+				<TimePicker
+					currentTime="0999-10-18T11:00:00"
+					onChange={ onChangeSpy }
+					is12Hour
+				/>
+			);
+
+			const yearInput = screen.getByLabelText( 'Year' );
+
+			// Verify initial input displays correctly
+			expect( yearInput ).toHaveValue( 999 );
+
+			// Change to year 500
+			await user.clear( yearInput );
+			await user.type( yearInput, '500' );
+			await user.keyboard( '{Tab}' );
+
+			// Verify input field value after change (human-readable, not zero-padded)
+			expect( yearInput ).toHaveValue( 500 );
+
+			// Verify onChange emits zero-padded ISO 8601 format
+			expect( onChangeSpy ).toHaveBeenCalled();
+			const lastCall =
+				onChangeSpy.mock.calls[ onChangeSpy.mock.calls.length - 1 ];
+			const outputDate = lastCall[ 0 ];
+
+			// Extract year from output and verify it's zero-padded to 4 digits
+			const yearMatch = outputDate.match( /^(\d{4})-/ );
+			expect( yearMatch ).not.toBeNull();
+			expect( yearMatch[ 1 ] ).toBe( '0500' ); // Explicitly verify zero-padded year
+
+			expect( outputDate ).not.toContain( 'NaN' );
+			expect( outputDate ).not.toContain( 'Invalid' );
+		} );
+	} );
 } );
@@ -139,7 +139,7 @@ export function setInConfiguredTimezone(
 		...updates,
 	};
 
-	const year = String( values.year );
+	const year = String( values.year ).padStart( 4, '0' );
 	const month = String( values.month + 1 ).padStart( 2, '0' );
 	const day = String( values.date ).padStart( 2, '0' );
 	const hours = String( values.hours ).padStart( 2, '0' );