He told WFPL that he decided to run as an independent because he doesn't feel Lundergan Grimes is offering liberals the candidate they deserve.
He said that he'll focus on the environment, poverty and gay rights in particular in his bid, and that while he believes Lundergan Grimes is a good Democrat, she "has had to take a conservative route for the campaign."
"I think Grimes has had to take a conservative route for the campaign," he says. "When I ran for Congress (the KDP) made me put out there I was a conservative Democrat, and I'm like 'Well, I'm not.' And they said you'll never win and I allowed them to do that. Then I said, hold on a second. We're not doing nothing but lying to people here,'" he told WFPL.
To join the ballot as an independent he has to change his party affiliation by Dec. 31 and submit at least 5,000 signatures to the state board of elections by August 2014.
Marksberry has never been considered much of a threat to Lundergan Grimes for the Democratic nomination, and hasn't picked up much support among local or national Democrats, despite entering the race long before her. He ran unsuccessfully against Rep. Brett Guthrie (R-Ky.) in 2010 and lost that race by nearly 35 points.
His bid as an independent, running to the left of Lundergan Grimes, could undermine her support among in the general election if he's able to draw away liberal voters to her campaign, and is likely to, at the very least, complicate her underdog attempt to unseat Sen. Mitch McConnell (R-Ky.) next year.
He suggested to WFPL those concerned with the prospect of his bid jeopardizing Lundergan Grimes's shot at toppling McConnell are "no better than McConnell."
"To those who think I'm a spoiler you have to ask yourself, what are you really trying to do here? Are you trying to make it a better place for everybody or are you just trying to get rid of McConnell at any cost. And if that's what you're doing then you're no better than McConnell," he said.