Wickremesinghe's United National Party says on its official Twitter account that Wickremesinghe took oath before President Maithripala Sirisena on Sunday.
The move promises to ease 50 days of political crisis, but could also be the beginning of a difficult cohabitation between the two leaders now in rival camps. A new Cabinet is expected to be sworn in soon, AP reported.
Sirisena abruptly sacked Wickremesinghe Oct. 26 and appointed former strongman Mahinda Rajapaksa in his place. Wickremesinghe insisted his removal was unlawful and Rajapaksa failed to get Parliament's approval.
The Supreme Court on Friday extended a lower court suspension of Rajapaksa, which forced him to resign on Saturday.