The Senate on Wednesday swore in Isaac Alfa, as the substantive senator representing Kogi East district.
Oath taking for the new senator was the first activity of the Senate for the day.
The development follows a Supreme Court judgment which affirms Mr Alfa as the senator representing the district.
With this, Atai Aidoko Ali, who has been representing the district until the oath-taking, ceases to be a senator.
Mr Alfa, at different times, accused Mr Saraki of partiality in his refusal to obey court order affirming him.