If the President resigns before the end of the term, the office of the President becomes vacant. In such an event, a special procedure should be followed as prescribed in Article 40 of the Constitution. To fill the vacant post of the President, Parliament should elect one of its Members as the President within one month from the resignation of the President. In the event of the President resigning from the post, the Parliament should meet within three days of the President’s resignation. At such a meeting, the Secretary-General of Parliament is required to inform the Parliament about the resignation of the President and fix a date to receive nominations for vacated President post.
If only one member of Parliament is nominated to the office of President, that individual shall be declared by the Secretary-General to have been elected to such office. If more than one person is nominated, a secret ballot should be taken, and the person should be elected by an absolute majority of votes cast. The Presidential Elections (Special Provisions) Act (No. 2 of 1981) sets out the procedure to be followed in electing a new President by the Parliament.
During the period between the President’s office becoming vacant and the assumption of office by the new President, the current Prime Minister functions as the Acting President. During this period, one of the Ministers of the Cabinet shall be appointed to act in the office of the Prime Minister. The newly elected President can hold the office for the remaining period.
This means, that in the event of Gotabhaya Rajapaksa resigning as the President, Ranil Wickremesinghe will become the Acting President for less than a month until Parliament elects a new President.