Xavier signed a one-year contract with the Pride of Rivers and the club completed his registration for this season.
The Senegalese completed his move alongside Ivorian midfielder, Alhassane Dosso, who also signed a one-year deal.
“We cannot say we scouted him because an agent brought him to Port Harcourt and after the coaches tried him out they saw the potential and began to work on his papers," Dolphins spokesman China Acheru said.
“The idea is to get a big squad with a lot of quality back up. This is what the coaches have been trying to do and we believe we will continue to build our squad as the weeks go by.”
Xavier last played for ASFA Yennega of Burkina Faso while Dosso played for the club between 2005 and 2008 before joining Sharks and then moving to Norway.
Dolphins have also completed the signings of Victor Alegbe and Ayobanmi Asekunuwo, both on season-long loans from Nigeria National League (NNL) side Wikki Tourists.
The Port Harcourt club will face Crown FC on Match Day 3 of the Glo Premier League this weekend.