“I’m here today to tell you that I’ve met with my supporters, we have had a great conversation and determined and decided that we can next make the best move, the best difference in the Commonwealth of Kentucky by running for the U.S. Senate," Grimes said.
Grimes was elected secretary of state in 2011, taking more than 60 percent of the vote. Before that, she served as a practicing attorney in Lexington. She is the daughter of former state Democratic Party chairman Jerry Lundergan.
McConnell brings to the race lots of seniority -- he is in his fifth term -- and lots of power and money as GOP leader. But he is not highly regarded in his home state and continues to draw strong and well-funded challengers despite Kentucky's conservative lean.
McConnell likely will have a huge financial advantage over whoever he faces in the general election, and his campaign team has earned a reputation for being ruthless.
Grimes is expected to tie the long-serving McConnell to Washington and argue that it's time for a change. She also played up her gender Monday, noting she is the only woman in statewide office in Kentucky.
"This Kentucky woman does not believe that the voters of Kentucky will be fooled that easily" by McConnell's campaign, she said.
Republicans immediately began tying Grimes to President Obama, who took less than 40 percent of the vote in Kentucky in 2012.
They noted recent comments in which a White House adviser suggested the administration should wage a "war on coal" -- a major part of the economy in Kentucky.
"Just last year, Alison Lundergan Grimes stood proudly at the Democratic National Convention to nominate Barack Obama, who has followed through on his promise to destroy the coal industry," said Rob Collins, executive director of the National Republican Senatorial Committee.
Grimes shrugged off the tactic and said voters have a choice between her and McConnell, not McConnell and Obama.
"Regardless of the vote that is issued in this race, we cannot change who our president is," she said. "But we can change who we have in Washington representing Kentucky."
Since actress Ashley Judd announced in March that she will not run for the seat, she and other big-name Democrats have focused their efforts on recruiting Grimes. Other Democrats who have said they won't run include Gov. Steve Beshear and Rep. John Yarmuth.
Grimes's rollout Monday was somewhat unorthodox. She delivered her remarks in front of a banner for her 2011 secretary of state campaign, spoke for just a few minutes and answered two brief questions before departing.
The entire press conference, which began more than half an hour late, lasted less than five minutes.
Updated at 4:28 p.m.