Richard Onyonka has been re-elected MP for Kitutu Chache South.
Last week, Nasa leader Raila Odinga endorsed the Ford Kenya candidate for the MP race.
Mr Onyonka won Tuesday’s by-election with 10,122 votes (45.86 per cent).
He will serve the constituency for a consecutive third term.
The constituency's Returning Officer Hilda Imbo declared him winner on Wednesday at 4am.
His party leader Moses Wetang'ula who spoke to the Nation on phone congratulated him saying he needs people like him in parliament to tame Jubilee's influence.
Antony Kibagendi came second with 5,074 votes (22.99 per cent) while Omwando Samwel Kenani came in third with 4,324 votes (19.59 per cent).
Maubi Andrew Mokaya got 2,191 votes (9.93per cent), Nyarango Henry Morara garnered 201 votes (0.91per cent), Onkangi James Kegoro got 100 votes (0.45per cent) while Mochoge Justus Onsongo 60 votes ( 0.27per cent)
Voting took place in all the 115 polling stations across the constituency.
The constituency had 59,017 registered voters and voter turnout was at 37.40per cent.
Valid votes were 22,072 while rejected ballots were 168.
Election was postponed in Kitutu Chache South constituency following the death of Jubilee candidate, Leonard Mwamba, two weeks to the August 8 polls.
Jubilee handed a direct ticket to Mr Kibagendi.
There was jubilation at St Mary's Mosocho Primary School tallying centre even before the results were officially announced after it emerged that Mr Onyoka had taken a commanding lead.
Hundreds of his supporters who had thronged the tallying centre broke into song and dance and lifted their MP-elect shoulder high.
The former assistant minister for foreign affairs walked into the polling centre at around 8.00pm and remained throughout the night as vote tallying proceeded.
Mr Onyonka, 55, will serve for a third term having won the seat in 2007 on a PDP ticket. In 2013, he won on an ODM ticket with 17,274 votes against his closest challenger Don Bosco Gichana who got 8,203 votes.
He took after his late father Zachary Onyonka who ruled the constituency from 1962 until his death in 1996.
He first ventured into politics after his father passed on prompting a by-election in which he lost.
During the senior Onyonka's time, the constituency was known as Kitutu Chache before being split into Kitutu Chache South and Kitutu Chache North.
Kitutu Chache North is currently held by Jimmy Angwenyi (Jubilee).