The Court of Appeal said the election was riddled with electoral malpractices.
Ugenya MP Christopher Karani has lost a second bid to retain his seat.
The Court of Appeal upheld the high court decision to nullify his election, citing electoral malpractices.
Justice Hannah Okwengu, who read the judgement in Kisumu on behalf of the three-judge bench, pointed out that the irregularities subverted the will of the voters.
Just like at the high court, Justice Okwengu indicated that the MP for Ugenya, Siaya County, and the Orange Democratic Movement fraternity engaged in a smear campaign against his predecessor, Mr David Ochieng, and the Movement for Democracy and Growth party.
She said they even went further to claim that Mr Ochieng was involved in the murder of former electoral commission ICT manager Chris Msando.
"In the circumstances of this case, I too found that the nature of the malpractices was very grave thus putting the election of the applicant in doubt; elections were validly nullified," Ms Okwengu ruled.
The other judges are Justice Erastus Githinji and Justice Jamila Mohammed.
High Court judge Tripsisa Cherere ruled that Mr Karani had profited from a "perverted" electioneering period.
Judge Cherere had directed Mr Karani to pay Sh3.5 million in costs but the Court of Appeal said each party should bear its own costs.
LESSON FOR ODM
Mr Karani said he will consult his lawyers on the next course of action.
"Since August I have not found time to serve my people because of the protracted court battle. But I want to assure my people that I am ready to go back to the poll and I will win," he said.
On his part, Mr Ochieng said the ruling should serve as a lesson to the ODM party.
"Rallying call of six piece is illegal and a way of subverting the proper right of [the] electorate who most of the time are illiterate. I look forward to meeting my opponent at the Supreme Court or the ground," Mr Ochieng said.