Onyango Oloo, who was TNA secretary general, has ditched Jubilee Party for ODM.
He did not reveal his reasons but sources said TNA's dissolution for the Jubilee merger made things difficult for him.
Oloo told the Star on Tuesday that he was finalising talks with leaders of the party under Raila Odinga's Cord coalition.
"We have had a series of consultative meetings. Soon, we shall make a formal announcement," he said.
Oloo played a key role in President Uhuru Kenyatta's presidential campaign in 2013.
He said he will move from Uhuru's party with several other officials.
Read: Overtaken by events: Court rules ex-TNA secretary general cannot hold two posts
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It was alleged that Oloo pulled one-man shows during his tenure as TNA secretary general but that his rivals in Jubilee had pledged to prevent this.
"For now I will not comment on the matter," he said.
Also read: TNA’s Oloo tells Luos how to return to power