Senator Peter Mositet has quit Jubilee Party after rejecting the just-concluded party nomination results.
Mr Mositet claimed the results favoured a political line-up led by one aspiring governor.
Senator Mositet, who was thrown out of a tallying centre in Maasai Technical Training Centre by police last week, termed the primaries as "a sham".
His rival, Philip Mpaayei, was declared winner with 62,067 votes against Mositet's 52, 022.
In a letter addressed to the JP Secretary General Raphael Tuju, and seen by The Standard, Mositet said the primaries were neither free nor fair.