The race was considered one of the country's most hotly contested in a district nearly evenly divided between Republican, Democratic and unaffiliated voters.
"Tonight, we are going to begin to hold the president and Don Rumsfeld accountable for the war in Iraq," Perlmutter told a crowd of supporters at the Golden West Marriott in Golden, the Denver Post reported. "Tonight is the night we bring change back to this country. Tonight is the night we bring hope back to this country and we can all begin to be proud again."
O'Donnell, who called Perlmutter to congratulate him on his win, said he had no regrets, according to the Post.
"We ran a great campaign," he said. "But it just wasn't enough in a bad year for Republicans, the worst year since Watergate."
Perlmutter will take the place of former Republican Rep. Bob Beauprez, who ran unsuccessfully for governor against Democrat Bill Ritter this year.
Colorado's 7th District covers parts of Denver and Jefferson, Arapahoe and Adams counties. Democrats spent $1.3 million for Perlmutter, while Republicans spent about $556,000, according to the two parties' congressional committees.
An article in the Denver Post in late October claimed the national Republican Party had begun shifting money away from O'Donnell and toward candidates in more competitive races throughout the country as polls showed him lagging behind Perlmutter in the lead-up to the election.
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