EMILY's List President Stephanie Schriock called Grimes an "energetic rising star" in a statement.

“She is an incredible leader who has fought for women and families by protecting victims of domestic violence, supporting state and local businesses, championing voting rights, and advocating for military personnel," Schriock said.

She added: "Mitch McConnellAddison (Mitch) Mitchell McConnellLawmakers feel pressure on guns Bipartisan group of House lawmakers urge action on Export-Import Bank nominees Curbelo Dem rival lashes out over immigration failure MORE is one of the least liked senators in the country for a reason – he’s hopelessly out-of-touch with the needs of his state. Alison is working tirelessly to make sure that Kentuckians’ voices are being heard."

EMILY's List raised $52 million last cycle, and the group's endorsement comes with access to its extensive donor network, as well as operational and campaign support.

Schriock penned an email to supporters alerting them to the endorsement that declares: "Believe it. We can beat Mitch McConnell in 2014," and notes his positions on women's issues.

The group has been paying close attention to Grimes' candidacy, and initially encouraged her to enter the race, so it's no surprise they're endorsing her in what will likely be the marquee race of the 2014 cycle.

But Grimes remains the underdog in the fight to unseat McConnell who, despite low popularity in the state, has amassed a nearly $10-million war chest at this point and has already launched ads hammering Grimes. A pro-McConnell super-PAC, Kentuckians for Strong Leadership, has also targeted Grimes with on-air attacks.