Former Nebraska Sen. Bob Kerrey (D) will run for the state's open Senate seat, two Democratic sources confirmed to The Hill, giving Democrats a fighting chance in a race they had previously been forced to write off.

Kerrey had announced earlier in February that he would not run, despite Democratic pleas for him to get in the race. Democrats were left without a viable candidate to hold on to Sen. Ben Nelson’s (D-Neb.) seat after Nelson said in December he would not seek reelection.

Word leaked on Monday that Kerrey had informed senior Democrats of his desire to run, but those reports were tempered by Democratic sources who said Kerrey was reconsidering, but had not made up his mind.

"Doing things the conventional way has never been my strong suit," Kerrey said in a statement on Wednesday, the day before the filing deadline. "I came to realize that my previous decision was the easy one, not the right one. My commitment to serve Nebraska and America, and to be part of the debate about the challenges we face was too strong to dismiss."

Kerrey's decision is a major coup for Democrats, whose prospects for holding on to control of the Senate are bolstered now that they have a competitive candidate in Nebraska, a conservative state where President Obama's poll numbers are underwater. The Republican primary for Nelson's seat has also worked in Democrats' favor, pitting the GOP establishment against the Tea Party wing and Sen. Jim DeMint (R-S.C.).

It was the second bout of unexpected good news for Democrats in two days as they worked to shore up their chances for holding on to the Senate. On Tuesday, Sen. Olympia Snowe (R-Maine), one of the most popular and centrist senators, announced she would retire, creating an opening for Democrats they never saw coming.

Democrats can only afford to lose three Senate seats in November and still maintain their majority in the upper chamber (if Obama wins reelection).

Republicans accused Senate Majority Leader Harry ReidHarry Mason ReidDems search for winning playbook Dems face hard choice for State of the Union response The Memo: Immigration battle tests activists’ muscle MORE (D-Nev.) of strong-arming Kerrey into the race in a backroom deal, dismissing Kerrey as far too liberal for the state he hopes to once again represent.

“As Nebraskans reacquaint themselves with Kerrey they will quickly recognize that living in Greenwich Village for so many years tends to change a person," said National Republican Senatorial Committee spokesman Brian Walsh. "Whether it’s his support for cap-and-trade, his advocacy for a government-run health care system or his desire to raise taxes on Nebraska small businesses, Bob Kerrey is a loyal supporter of the Obama agenda and he’s simply out-of-step with Nebraska.”

It was not a smooth campaign rollout for Kerrey, whose previous decision not to run led a fellow Democrat to quit his job. Chuck Hassebrook jumped into the Democratic primary after Kerrey said he wouldn't run, but had to resign as a member of University of Nebraska's Board of Regents in February to do so. Because of the filing deadline, he can no longer reclaim his old job. 

Hassebrook had responded to initial reports of Kerrey reconsidering on Monday by saying he didn't believe it and that Kerrey had given him his word.

"Bob Kerrey is a man of integrity. He told me as recently as a few days ago that he would assist my campaign," Hassebrook said in a statement.

Kerrey's campaign manager, Paul Johnson, told The Hill that Kerrey had spoken to Hassebrook by phone and email about his decision to enter the race. 

Before Kerrey announced in early February he wouldn’t run, Republicans had already launched an attack, dubbing him a carpetbagger because he had moved from Nebraska to New York, where he led the New School.

The former governor of Nebraska, Kerrey is a decorated Vietnam veteran and former chairman of the Democratic Senatorial Campaign Committee. He said on a website launched Wednesday that the future of the country required a renewed focus on fiscal discipline.

"Our future requires a commitment to fiscal discipline and restoring America as the land of opportunity. Party-first, me-first, and politics-first created the mess," Kerrey wrote. "A commitment to country first will get us out. I hope you will join me on this mission."

—This post was updated at 3:07 p.m.