Ms. Nunn, the daughter of former Democratic Sen. Sam Nunn of Georgia and CEO of the Points of Light volunteer organization, said her father has served as a role model, showing her what can be done by "working with others to solve problems and keep our country safe."
"But the Washington that my father worked in not so long ago is a place that just doesn't exist anymore," Ms. Nunn said in an email blast to supporters. "Instead of searching for common ground and working together to create solutions, too often our political leaders are simply trying to win the latest battle. Meanwhile, we are running up our national debt and failing to make tough choices to secure our economic future."
The National Republican Senatorial Committee welcomed Ms. Nunn to the race by saying that she "proudly" embraces President Obama and the "liberal agenda" that most red state Democrats shy away from.
"Those who know Michelle Nunn agree that politically she is a liberal in the mold of Chuck Schumer, Nancy Pelosi and Barack Obama who supports Obamacare, higher taxes, and a bigger more invasive government," said Brad Dayspring, NRSC spokesman. "It takes more than just family ties to get elected to the Senate and we look forward to a robust debate about the Obama/Nunn agenda and the ramifications that it has on middle-class families and women in Georgia."
Ms. Nunn is the second Democrat to enter the race. Branko Radulovacki, a psychiatrist, announced last month that he also is seeking to replace retiring Sen. Saxby Chambliss, a Republican.
The Republican field is crowded with Reps. Paul C. Broun, Jack Kingston and Phil Gingrey and former Georgia Secretary of State Karen Handel among those vying for the GOP nomination.
The race is key to Republicans' chances of capturing control of the Senate. The GOP needs a net gain of six seats to take over the chamber, and the 2014 map appears to be working in their favor
Republicans are well-positioned to pick up three seats in South Dakota, West Virginia and Montana, thanks to the retirements of Democratic senators.
The attention of the political world is now focused on the races in Alaska, Arkansas, Louisiana and North Carolina, where Democrats are defending seats.
Democrats, though, hope they can put Republicans on the defense in Kentucky, where Secretary of State Alison Lundergan Grimes is challenging Senate Minority Leader Mitch McConnell, a Republican.
Charles S. Bullock, political science professor at the University of Georgia, said Ms. Nunn faces an uphill battle, noting that Democrats have not won a statewide race there since 1998.
"It is Republicans to lose, but as you have seen in the last two election cycles, Republicans can lose things they should win," Mr. Bullock said.
Mr. Bullock said Ms. Nunn could benefit from an easy Democratic primary and a divisive Republican race, where the candidates could "beat up on each other."
Charlie Cook, publisher of the Cook Political Report, said the best bet for Mrs. Nunn, a political newcomer, is for Republicans to elect a flawed candidate, much like they did in the 2010 and 2012 Senate races.
"Nunn's candidacy, it really sort of matters only if Republicans nominate, how do I say this, an exotic or potentially problematic nominee," Mr. Cook said. "That is the term I use with my wife, who has been trying to convince me not to use the term 'wacko' anymore. If Republicans nominate a sort of normal-chromosomal-alignment Republican, they hold onto the seat."