Migori Senator Wilfred Machage has decamped from the Orange Democratic Movement to the Democratic Party.
Dr Machage announced on Friday that he will leave the Senate to run for the Kuria West parliamentary seat seat on a DP ticket.
Dr Machage, however, declined to reveal if he had written to ODM, which sponsored him to the Senate, to notify the party of his departure.
"Those are details," Dr Machage said during a press conference in Nairobi.
He said parties that consider themselves popular will be shocked to learn that they have few lawmakers after the August 8 General Election.
"Let the other parties not boast because of changed laws that give them more funds," he said.
DP leader Joseph Munyao said the party would field candidates for all positions, except the presidency, in all counties.
He said DP will not merge with any other political parties before the polls.
Dr Machage's defection has been largely interpreted to be a response to fears that he might not be re-elected on an ODM ticket, following concerns that he has not been an ardent supporter of the party.
The lawmaker, for instance, was not on the frontline when ODM leaders took to the streets to push for the removal of the Issack Hassan-led electoral commission team last year.
In the last General Election, the lawmaker was a beneficiary of a political agreement in which a candidate from the Kuria community was to take Migori County's Senate seat, leaving the gubernatorial seat for the Luo.
However, Governor Okoth Obado, who defeated an ODM candidate on a People’s Democratic Party ticket, has declared his support for Mr Odinga and is seeking to rejoin ODM ahead of the August polls.
Luo residents in Migori are also not willing to honour the political agreement due to claims that the community, the majority in the county, has been short-changed.