High Court sitting in Eldoret on Tuesday morning nullified elections of Jubilee rebel Kangongo Bowen of Marakwet East, citing irregularities and illegalities during the August poll.
Sammy Kipkui, a voter, had challenged the outcome in the tight race that saw Bowen beat anti-FGM crusader Linah Kilimo.
Last year, presiding Judge Kanyi Kimondo ordered recount in four major polling stations against Bowen's wishes.
While delivering the judgment, Kimondo said: "The court is convinced that the first respondent committed illegalities and irregularities."
"I hereby declare the outcome of the election null and void. I further order fresh elections in the said constituency."
Returning Officer Martin Wekesa, declared Bowen the winner with just a slim margin of 967 votes in the closely contested race.
Last month, Bowen was one of Jubilee MPs kicked out from Environment committee as Vice Chair after order from State House.
Kilimo, a one time Assistant Minister, contested as an Independent candidate after losing in Jubilee primaries.
The MP will be required to pay Sh 2 million as instruction fee while the court shall refund the petitioner Sh500,000.