Ohuabunwa polled 135 votes to defeat his closest rival, Rep. Uko Nkole, who scored 29 votes.
Other contestants, including Mr Mba Ajah and Dr Igwe Orji, polled 10 and nil votes, respectively with one void vote.
There were 175 accredited delegates from Arochukwu, Bende, Isuikwuato, Ohafia and Umunneochi Local Government Areas that make up the district.
The News Agency of Nigeria (NAN) reports that Ohuabunwa was a member of the eighth Senate but lost his second term bid in 2019 to Sen. Orji Kalu.
Nkoli, who currently represents Arochukwu/Ohafia Federal Constituency, sought to move to the Upper Chamber.
NAN reports that the three-member ad hoc delegates election, which earlier took place at the Ohafia Local Government Headquarters on Tuesday, ended in fiasco.
A free-for-all had erupted between supporters of the two contestants, over the alleged non-qualification of some delegates at a time Isuikwuato delegates were voting.
However, the Chairman of the Electoral Committee, Chief Silas Okafor, told newsmen in Umuahia on Wednesday that the exercise was later concluded, in spite of the disruption.
“What happened was that during the vote counting, supporters of one of the aspirants tried to stop the process, when they noticed that their person was trailing behind.
“However, the process was successfully concluded and Sen. Mao Ohuabunwa, who polled 135 votes, is declared winner,” Okafor said.
Meanwhile, Ohuabunwa said he dedicated his victory to God and his constituents, promising not to disappoint them.
He stated this in a statement issued in Umuahia, urging his co-contestants to join him as members of one family.
He promised to carry everyone along.