Rounds will most likely challenge Democrat Tim Johnson, who currently holds the seat but hasn't officially made an announcement yet to run for a fourth term.
PIERRE, S.D. — Former South Dakota Gov. Mike Rounds said Thursday that he will run for the U.S. Senate in 2014.
The former Republican governor's announcement was widely expected, as he said in September that he was forming a committee to explore a run for the seat held by Democratic Sen. Tim Johnson.
Johnson, 65, hasn't officially announced whether he will seek a fourth term. But he released a statement Thursday saying he intends to "put together a winning campaign in the weeks and months ahead," and that his formal announcement will come next year.
Rounds, 58, said at a news conference Thursday that he wants to end the gridlock in Washington, reduce the federal deficit and straighten out health care reform.
"We need to become a country of cooperation instead of confrontation," he said.
Rounds was a state senator from 1991 to 2001 before serving two terms as governor from 2003 to 2011. After leaving office in early 2011, Rounds served as president and CEO of an insurance and real estate company based in Pierre.
Johnson was elected to the U.S. House in 1986 and to the Senate in 1996. He was re-elected in 2002 and 2008. He also previously served in the state Legislature.
The state Democratic Party immediately mounted a defense after the morning announcement. Party Chairman Ben Nesselhuf called Rounds a "nice guy with the wrong priorities" for South Dakota.
Johnson was more complimentary.
"I had an excellent working relationship with (Rounds) during his eight years as Governor, and the fact that he has already re-stated his refusal to take the Grover Norquist 'no tax increases under any circumstances' pledge is a very good sign," Johnson said in a statement.
But he added that he still feels great and has work to do.
"In the meantime, I intend to continue to focus on my important work representing South Dakota," he said.
Johnson defeated prostate cancer in 2004 and had surgery in December 2006 to stop bleeding in his brain. He was diagnosed with arteriovenous malformation, a condition that causes arteries and veins in the brain to grow abnormally large, become tangled and sometimes burst.