Turkish President Ahmet Necdet Sezer approved legal changes that open the way for Recep Tayyip Erdogan, leader of the ruling party, to run for parliament and take over the post of prime minister.
Erdogan was barred from public office because of a jail sentence in 1999 for inciting religious hatred. He can now stand for election in February.
Sezer's Web site said he had ratified the constitutional changes. He vetoed them earlier, but parliament, dominated by Erdogan's Justice and Development Party, passed them again.