SEOUL—South Korea’s legislature voted to impeach acting President Han Duck-soo on Friday after he declined to make judicial appointments needed to advance the impeachment of his predecessor, extending the political upheaval that began with a short-lived martial law declaration earlier this month.

South Korea's opposition-controlled National Assembly voted to impeach acting President Han Duck-soo despite vehement protests by governing party lawmakers, further deepening the country's political crisis.

As the president awaits an impeachment trial, the country’s interim leader may, too, be ousted. The currency has plunged as the crisis has deepened.