Pawlenty made the announcement in a video on his website in a preview of a formal announcement on Monday.

"Tomorrow my first campaign stop will be in Iowa and that's where I'm going to begin a campaign that tells the American people the truth," Pawlenty said in the video. "I'm Tim Pawlenty and I'm running for president of the United States."

Pawlenty, known as "T-Paw" to his supporters, was a popular two-term governor in a big swing state, giving him credibility as a Republican who can attract vital support from independent voters.

Pawlenty announced in March that he would set up a presidential exploratory committee. He was the first senior Republican to do so.

Former Massachusetts Governor Mitt Romney has been leading some early polls for the Republican presidential nomination. Newt Gingrich, a former speaker of the U.S. House of Representatives who entered the race two weeks ago, has had a rocky start having drawn the ire of fellow conservatives by criticizing a Republican plan to overhaul the Medicare health insurance program for the elderly.

Prominent Republicans such as Indiana Governor Mitch Daniels, former Arkansas Governor Mike Huckabee and Mississippi Governor Haley Barbour have decided not to join the race.

Two potential candidates with ties to the conservative tea party movement, U.S. Representative Michele Bachmann and 2008 vice presidential nominee Sarah Palin, have not announced their plans.