The Democratic incumbent held a 51 percent to 47 percent for his Republican challenger with 73 of Colorado's precincts tallied, CNN reported.
By the time the networks called the Colorado race for Obama, the president had already been projected the winner of a second term in office. Another swing state, Ohio, put the president over the top.
Colorado put Obama at 290 electoral votes. He needed 270 to win the election.
In the state's U.S. House races, GOP incumbent Scott Tipton defeated Democratic challenger Sal Pace, CNN projected. With 54 percent of the vote tabulated, Tipton led 54-40, CNN said.
In the 6th District, incumbent Republican Mike Coffman also knocked off his Democratic challenger, Joe Miklosi, CNN projected. The margin was 50-44 with 62 percent counted.
The Colorado House appeared the cusp of changing political hands, The Denver Post reported. Early returns had Democrats leading Republican incumbents in at least three key races.
The GOP held only a 33-32 majority going into the elections.
If Democrats succeed in regaining the majority, Mark Ferrandino of Denver is expected to become the first openly gay speaker of the Colorado House, the Post said.
In the state Senate, where the Democrats had held a 20-15 majority, the balance of power was still up in the air, the Post said.