During his long career, 71-year old Obey has only faced serious opposition a couple times in representing Wisconsin's 7th District -- a seat he's held since 1969. But recently, two political publications, CQ Politics and The Rothenberg Political Report moved the race as definitely Democratic to likely Democratic.
At a press conference on Capitol Hill, Obey said, “"There is a time to stay and a time to go. And this is my time to go."
He added that he’s also just “bone-tired.”
Duffy has been benefiting from media buzz including a New York Times article spotlighting the race, Time Magazine naming him one of the "10 More Scott Browns," a reference to now Republican Sen. Scott Brown's upset in the Massachusetts special election to fill Ted Kennedy's seat.
The Ashland, Wisconsin district attorney has been hitting hard on Obey backing the stimulus bill.
He has also been running a strong online component to his campaign, starting with a flashy and creatively put together website, inviting readers to "Roll with Sean." Obey only put up his campaign site up in March.
On his website, Duffy notes that he is a fourth generation lumberjack athlete, winning three-time world championship in the 90-foot speed climb. He says he's also an accomplished log-roller.
And he is no stranger to the spotlight, 38-year old Duffy's also been a commentator for ESPN's "Great Outdoor Games." He first gained attention as a participant on MTV's "The Real World," Boston edition.
Duffy lives in Wisconsin with his six children and wife Rachel Campos, another MTV reality show alum.
Potential 2012 GOP presidential candidate and Minnesota Gov.Tim Pawlenty recently held an online contest that Duffy won, bringing more money and support to his campaign. And former Alaska governor and Republican vice presidential candidate Sarah Palin has come out backing Duffy.
The National Republican Congressional Committee responded to the Obey news, "There is no question that David Obey was facing the race of his life and that is why it is understandable that the architect of President Obama's failed stimulus plan has decided to call it quits, said NRCC spokesman Ken Spain.
Rep. Chris Van Hollen, D-Md., the Democratic Congressional Committee chairman said, “Chairman Obey would have won re-election again had he run. We are confident that a Democrat who shares Chairman Obey’s commitment to making progress for Wisconsin’s middle class families will succeed him as the next Representative of Wisconsin’s 7th Congressional District."
Obey, who has been in Congress longer than Duffy has been alive, took veiled swipes at the district attorney during his press conference on Capitol Hill, although without actually mentioning Duffy by name. The chairman said he thinks his district is ready for somebody new, not somebody “who poses as a fresh face,” saying that some of Duffy’s positions he thinks are recycled from Presidents Ronald Reagan and George W. Bush. Obey noted his district deserves someone who focus on working people and not use “slick words” and an “actor's ability.”
Duffy responded to Obey's announcement in a statement, "While Congressman Obey and I have major differences on the issues, he has dedicated his life to be a servant for his state and his country and for that he should be commended."
"He has served honorably as a Congressman for more than four decades and he deserves a great deal of respect for his work. I wish Mr. Obey and his family well in their future endeavors," Duffy said.
As Wisconsin's longest-serving congressman, Obey currently holds one of the most powerful positions in Congress as chairman of the Appropriations Committee. Back home, he's a local political establishment with buildings named after him around his district.
Obey said he was not leaving office because of a threat of losing to Duffy.
“Let me put it this way, I’ve won 25 elections, does anybody really think I can’t win another one?” The congressman said he’d been thinking of retiring for a long time, but says he stayed after seeing stubbornness of the Bush administration after a meeting at the White House after September 11, 2001.
Obey was once a young up-and-coming politician himself. He was just 30-years old when elected to the House, and at the time was the youngest member of Congress upon taking his seat.
Obey's announcement came as a big surprise to his colleagues, sources tell Fox Obey did not give an early warning to the caucus about his decision.
FOX News' Chad Pergram contributed to this report.