Craig, R-Idaho, asked a Minnesota court to allow him to withdraw his guilty plea stemming from a sex sting in a men's bathroom at the Minneapolis-St. Paul International Airport. The judge Thursday denied his request.
Craig in a statement said he was "extremely disappointed" with the ruling, CNN reported.
"I am innocent of the charges against me. I continue to work with my legal team to explore my additional legal options," Craig said. "I will continue to serve Idaho in the United States Senate, and there are several reasons for that."
In his 27-page ruling, Hennepin County District Judge Charles Porter found Craig entered his guilty plea accurately, voluntarily and intelligently.
"The evidence supports a conviction for disorderly conduct," the opinion read.
While the plea lacked a judge's signature, Porter said the signature's absence was not a fatal flaw.
Craig originally said he intended to leave the Senate Sept. 30, then later said he would retain his seat until after the matter was adjudicated.