Sirisena appointed Rajapaksa along with several other legislators to the cabinet.
Sri Lanka President Maithripala Sirisena appointed newly appointed Prime Minister Mahinda Rajapaksa as the finance minister, the president's media division said on Monday.
He also appointed Rajapaksa along with several other legislators to the cabinet.
Sirisena on Friday night had sacked Wickremesinghe and appointed Rajapaksa as the new prime minister in a surprise move that is being debated as a constitutional coup.
Sirisena also suspended Parliament till November 16 after Wickremesinghe sought an emergency session to prove his majority.
Rajapaksa was defeated in the 2015 presidential election by Sirisena who had the backing of Wickremesinghe's UNP. After a unity government, the political relationship soured between the two, leading to Wickremesinghe's sacking by Sirisena.