Senior Congress leader Satpal Maharaj resigned from the Congress on Friday and joined the Bharatiya Janata Party (BJP) in the presence of its national president Rajnath Singh in New Delhi.
The Paudhi Garhwal MP said he was joining the BJP to strengthen the country, which now has a leader in Narendra Modi, the party's prime ministerial candidate.
"I want India to grow and outsmart China in development and this is only possible when an able leader like Narendra Modi becomes the prime minister," he said.
He said that after the flash floods in Uttarakhand in June last year, the people have been suffering and loyal Congress workers were being sidelined.
Rajnath Singh welcomed him in the party fold and said he would be given all the rewards he deserves.
The senior leader has been sulking for some time after he was sidelined.
His supporters said Maharaj was "feeling suffocated" in the party.
Maharaj has a massive following in the hill state and elsewhere because of his religious sermons, and was first angry at being sidestepped and Harish Rawat being appointed the chief minister.
His wife Amrita Rawat is a Congress legislator. The fate of the Congress government in the hill state is also likely to be challenged by Satpal Maharaj's exit as 10 legislators are from his camp, sources said.