Freshman Rep. Parker Griffith (D-Ala.) announced Tuesday afternoon he will switch to the GOP, citing the Democratic agenda as his reason.
Griffith said Democratic legislative priorities, including healthcare reform, are harmful to the country.
Griffith added that he has always considered himself an "independent voice" but that the differences in the two parties are now too vast for him to remain a Democrat.
Sources tell The Hill that GOP lawmakers in the Alabama delegation, including Rep. Robert Aderholt, began wooing Griffith several weeks ago.
House Republican Whip Eric Cantor (R-Va.) welcomed Griffith to the GOP.
"When a member of Congress decides to leave a 258-seat majority to join a deep minority, it is a sure sign that the majority party has become completely disconnected from seniors, young workers and families in America," Cantor said in a statement.
Griffith occupies one of the most conservative districts held by a Democrat. He replaced Democratic Rep. Bud Cramer (Ala.) in a seat that has stayed Democratic even as the South has trended Republican in federal elections.
Despite his vulnerable district, Griffith had yet to draw a top-flight GOP challenger. Madison County Commissioner Mo Brooks and businessman Les Phillip each raised modest amounts of money for the race, with Phillip self-funding a little bit.
Griffith has bucked his party on nearly all of the items at the top of its legislative agenda.
This month he voted against the Democrats' bills on financial regulatory reform and the estate tax, as well as the omnibus. He was one of four Democrats to oppose healthcare reform, climate change and the stimulus package. The others were Reps. Bobby Bright (Ala.), Walt Minnick (Idaho) and Gene Taylor (Miss.).
Griffith said in August that he would not back Nancy Pelosi (D-Calif.) for House Speaker again because she is too divisive.
"I would not vote for her. Someone that divisive and that polarizing cannot bring us together," he told the Huntsville Times. "If she doesn't like it, I've got a gift certificate to the mental health center."
The White House appeared to be caught unaware. At the end of the daily press briefing, White House Press Secretary Robert Gibbs said he did not know that Griffith was switching parties.
Matters have not always been so friendly between Griffith and the Republicans.
During the 2008 campaign, the National Republican Congressional Committee (NRCC) launched an attack on Griffith, who is a physician, accusing him of "warehousing" cancer patients and "under-dosing" them so he could boost his profits.
"Parker Griffith: Shameful conduct. He can't be trusted," concluded the ad. (The ad, which was posted by The NRCC's YouTube account is no longer available. A message says: "This video has been removed by the user.").
But Alabama Republican Party Chairman Mike Hubbard welcomed him to the GOP.
“It was a pleasant surprise when Congressman Griffith called me this morning to inform me that he is leaving the Democrats to become a Republican," Hubbard said in a statement Tuesday.
Griffith won the open 5th district by a mere 4 percent in 2008; Sen. John McCain (R-Ariz.) carried the district with 61 percent in the presidential election.
His announcement comes after four House Democrats in recent weeks declared they would retire without seeking higher office: Reps. Dennis Moore (Kan.), Brian Baird (Wash.), John Tanner (Tenn.) and Bart Gordon (Tenn.).
Republicans now view those four seats as pickup opportunities for the 2010 midterm elections.
Rep. Patrick McHenry (R-N.C.) welcomed Griffith to the Republican conference via Twitter on Tuesday.
"Welcome aboard!" wrote the congressman on his account.
Griffith sits on three committees: Science and Technology; Small Business; and Trasportation and Infrastructure. Griffith's defection will result in 257 Democrats and 178 Republicans in the lower chamber.
— Aaron Blake, Bob Cusack, Molly K. Hooper and Sam Youngman contributed to this post.
— This story was originally posted at 11:06 a.m.