"If I'm called a yellow journalist, immoral, a liar — as a matter of fair play, I did a little research on him, and he's got some views and friendships that have not been fully vetted," Hannity said in an interview Friday. "He sparked it. He initiated it."
He denied that he was out for revenge.
"I follow my gut and instincts on what interests me," he said. "The fact that a congressman wants to start a fight with me, that's his business. I have the ability to fight back, and I will."
The spat could prove a welcome jolt of interest for Hannity when cable news ratings are sagging months since the presidential election. Hannity's average viewership of 1.9 million people in February was down 11 percent from February 2012, with a much sharper decline among young viewers, the Nielsen ratings company said.
Hannity said his ratings have been stabilizing. His Thursday night show, which featured Washington Post writer Bob Woodward, drew 2.5 million viewers.
Media critic Howard Kurtz, of The Daily Beast, said it was Ellison who had picked the fight and suggested he may have been trying to seek attention.
Ellison was unavailable for comment Friday, his spokesman said. In a statement issued Thursday, Ellison criticized Hannity's "personal attacks."
"Representative Ellison was invited to appear on 'Hannity' to discuss the sequester, an issue that will harm thousands of his constituents and the American economy, and accepted the invitation for that reason," spokesman Jeremy Slevin said.