Ugenya MP Chris Karan has lost his seat following a successful petition by his rival David Ochieng.
The High Court in Kisumu on Thursday ruled that Mr Karan's campaign was "perverted"., and that the entire August 8, 2017 in Ugenya was "compromised".
Mr Karani suffered a double blow as the judge ordered him and other respondents to pay Sh7 million in costs.
The verdict followed Mr Ochieng’s argument that his campaign was hampered after he was accused of having a hand in killing of IEBC ICT Manager Chris Msando.
The judge ruled that Mr Karani profited from a “perverted” vote chase.
She said Mr Ochieng, who was defending his seat, had successfully convinced the court that he could not seek votes because Mr Karani poisoned the environment.
“I find that the campaign was perverted and compromised the integrity of the election,” the judge ruled in a packed courtroom.
“Being Siaya was Raila Odinga’s backyard, linking Mr Ochieng to Jubilee affected the final results. These results did not pass transparent and verifiable-election test.”
Mr Ochieng defected from ODM, on whose ticket he had won the March 4, 2013 poll, and formed his own party, Movement for Democracy and Growth.
But in the run-up to the elections, Mr Msando was mysteriously murdered and his body dumped in Kikuyu alongside that of his female friend.
Mr Msando hailed from Ugenya and his death upset many residents of Siaya, the home county of Nasa leader Raila Odinga.
The MP was also accused of undertaking projects sponsored by the Jubilee Party in Ugenya, an ODM stronghold.
Facing hostility and unable to traverse the county in vote hunt, Mr Ochieng eventually lost the race.
He went to the High Court, not to disputed the figures announced but the process.
This court decision mimics that of the Supreme Court, which nullified the presidential election after finding the electoral process could not be verified.
Mr Ochieng said the smear campaign whipped up emotions among the people, making it difficult for him to campaign.
He claimed that Siaya Senator James Orengo led the campaign to mudsling him