The Senate Conservatives Fund has long been critical of McConnell arguing that the top Senate Republican does not sufficiently oppose Obamacare.
The Bevin endorsement is one of the earliest endorsements the conservative organization made this cycle. A day earlier the group endorsed Mississippi State Sen. Chris McDaniel (R) shortly after he announced his primary challenge to Sen. Thad Cochran (R-MS).
The McConnell campaign slammed the endorsement.
"Matt Bevin now has the dubious honor of standing with a self-serving DC fundraising group that made its name by recruiting and promoting unelectable candidates that ensured Barack Obama a majority in the Senate," McConnell spokesman Allison Moore said in a statement. "They clearly care less about Kentuckians than they do about their reputation for supporting laughably bad candidates. Now they can add a New England bailout recipient who claims he went to MIT to their roster of notable failures."
The MIT mention refers to Bevin's education record. Earlier in the year The Hill reported that Bevin exaggerated his ties to the school. The McConnell campaign has aired campaign ads attacking Bevin on this.