Vijaykumar said he would hit the campaign trail as and when advised by the BJP high command.
"I am known in all the southern states by virtue of my acting in all the regional language movies. People in Tamil Nadu know me well," the actor, who joined the party in the presence of Union Minister Pon Radhakrishnan, told reporters.
He hailed Prime Minister Narendra Modi and his government's many schemes and said they should reach all states.
To a question, he said he had not joined the party with an eye on fighting polls, but wanted to do his bit to propel the BJP to the ruling saddle in Tamil Nadu, where Assembly polls are scheduled on May 16.
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Radhakrishnan said the party "wholeheartedly" welcomed the veteran actor.
Vijayakumar joining BJP would be helpful for the party all over south India, he said in an apparent reference to the actor being well-known among southern region movie-goers.
"This will enable more artistes to join BJP," he said.