Coleman has 10 days to appeal to the state Supreme Court. Once the petition is filed, it could further delay the seating of Minnesota's second senator for weeks.

"It's time that Minnesota like every other state have two" senators, a jovial Franken said outside his Minneapolis townhouse with his wife Franni at his side. "I would call on Senator Coleman to allow me to get to work for the people of Minnesota as soon as possible."

After a statewide recount and seven-week trial, Franken stands 312 votes ahead. He gained more votes from the election challenge than Coleman, the candidate who brought the legal action.

The state law under which Coleman sued required three judges to determine who got the most votes and is therefore entitled to an election certificate, which is now on hold pending an appeal.

"The overwhelming weight of the evidence indicates that the November 4, 2008, election was conducted fairly, impartially and accurately," the judges wrote. "There is no evidence of a systematic problem of disenfranchisement in the state's election system, including in its absentee-balloting procedures."