Hours later Republican Norm Coleman conceded the race, giving Democrats a 60-seat majority in the Senate that potentially makes the party filibuster proof.
In a victory news conference Tuesday afternoon, Franken said he wanted to represent all Minnesotans -- not just those who voted for him.
"I’m not going to Washington to be the 60th Democratic senator," he said. "I’m going to Washington to be the second senator of the state of Minnesota."
Earlier, Coleman congratulated Franken publicly in a news conference in St. Paul. He said he called the new senator-elect.
"It's over and we should all work together to support our new United States Senator," Coleman said.
In a statement, President Barack Obama said: "I look forward to working with Senator-elect Franken to build a new foundation for growth and prosperity by lowering health care costs and investing in the kind of clean energy jobs and industries that will help America lead in the 21st century."
The latest developments came after the state's top court Tuesday unanimously rejected Coleman's claims that inconsistent practices by local elections officials and wrong decisions by a lower court had denied him victory.
"Al Franken received the highest number of votes legally cast and is entitled [under Minnesota law] to receive the certificate of election as United States Senator from the State of Minnesota," the court wrote.
In upholding a lower court ruling in April, the justices said Coleman had "not shown that the trial court's findings of fact are clearly erroneous or that the court committed an error of law or abused its discretion."
Coleman, the incumbent, initially led the former Saturday Night Live funnyman after the November, 2009 election. But subsequent challenges and recounts eroded Coleman's lead and but Franken on top. Minnesota Gov. Tim Pawlenty, a Republican, said he will abide by the decision.
"The bottom line is that's history, I'm not looking back, I'm not questioning what's counted and what's not counted," Coleman said. "The [Minnesota] Supreme Court has decided. We are a nation of laws."
Franken said Coleman was "gracious" in his phone call, and told him "it's going to be the best job you'll ever have."