The Court of Appeal has nullified the election of Alfred Mutua as Machakos Governor in the August 2017 vote.
Judge William Ouko said the IEBC's declaration of Mutua as the winner of the August 2017 vote was not valid.
"The results as declared by the returning officer failed the constitutional test," he said on Friday.
The appellate court set aside the judgement by the High court in the petition filed by Wiper's Wavinya Ndeti.
Justice Ouko said the election was not conducted fairly and directed the IEBC to conduct fresh polls.
The judges further ordered Mutua of the Maendeleo Chap Chap party and IEBC to pay the costs of Wavinya's appeal.
The appeal was heard by judges William Ouko, Mohamed Warsame, and Gatembu Kairu
In February, the High Court sitting in Machakos upheld the election of Mutua dismissing allegations made by Ndeti.
Justice Aggrey Muchelule, when he gave a ruling, said the petition lodged by Ndeti lacked merit.
"The petition lacks merit…the Independent Electoral and Boundaries Commission (IEBC) conducted a free, fair and credible election," the judge said then.
However, the Court of Appeal judges said the trial court erred in holding that the governor was validly declared as the winner.
The court faulted the IEBC for using Form 37C instead of using cumulative results from Form37A in declaring the win.
Ndeti, in her petition, accused Mutua of using county resources - including vehicles and funds, to campaign for his re-election contrary to laws governing elections.
After the ruling, Mutua told his supporters to stay calm saying: "I know I will be the fifth president of this country."
"I am not worried at all since I know I was validly elected. I will move to the Supreme Court and get a stay of this judgement."
The governor said he is still in office will continue to discharge his duties as Machakos governor.
"I want to tell my people they did nothing wrong in the election, These are hurdles one goes through before being lifted to the next office," Mutua said.
Ndeti, for her part, said she is ready to go back on the ground so that "Machakos voters reaffirm their choice of governor."
"Let Mutua swallow his pride like I have done in the past. I will meet him in the campaigns," Wavinya said.
The former Kathiani MP said she does not mind Mutua challenging the appellate decision at the Supreme Court.
"I will take my appeal to my father in Heaven in prayer and will still win the seat," she said.
She asked IEBC to prepare to hold a free, fair, and credible election that gives the Machakos people an opportunity to elect their governor.
"I just want IEBC to do their job. I am ready to face Mutua and square it out in a new election," she added.