Dean, in a conference call with reporters, also batted away questions about logistical challenges and added costs the change would produce, saying those things would be worked out in the coming weeks.
Obama, speaking to reporters in St. Louis, said he was excited about the move.
"Sometimes our conventions don't feel like they are open to everybody," Obama said. "For us to be able to do it in Invesco Field is an opportunity for 80,000 people who might otherwise not have been able to participate to get involved."
It won't be the first time a presidential candidate has accepted the nomination in a stadium. On July 15, 1960, John F. Kennedy gave his acceptance speech before tens of thousands at the Los Angeles Coliseum.
Separately, one official confirmed that Obama's aides were attempting to arrange a speech at a second dramatic venue: Berlin's Brandenburg Gate, part of Obama's July trip to Europe and the Middle East.
The Gate was the site of one of Ronald Reagan's most memorable speeches. On a trip in July 1987, Reagan stood before throngs of West Berliners and implored then Soviet President Mikhail Gorbachev to tear down the Berlin Wall dividing the city. The wall is no longer there.
Ron Perea, Secret Service special agent in charge in Denver, declined to discuss what security precautions the agency would take for the convention's open-air event, including any restrictions on airspace and traffic.
Most of the convention will take place at the 21,000-seat Pepsi Center. Construction for the convention was beginning there Monday amid concerns about lagging fundraising and cost overruns.
Last month, the convention's host committee reported it was nearly $12 million short of the $40.6 million it had pledged to raise for the effort. Host committee members spoke openly of needing the Obama campaign's help to close the gap.
Dean said the convention was operating on budget, and Obama senior adviser Anita Dunn said the campaign was on board to help.
"The fact that the nomination was not decided until the begining of June - clearly many donors would have hung back a little to see if the candidate of their choice was going to get the nomination," Dunn said.
With an influx of younger voters and Hispanics in recent years Colorado, once heavily Republican, is among a handful of states in the mountain West that have been trending Democratic. Both parties view it as a general-election swing state; Republican John McCain kicked off a five-day economy-focused campaign swing in Denver Monday.
Matt Burns, a spokesman for the Republican convention, dismissed the new speech locale as "stagecraft and theatrics" that "isn't the kind of change the American people deserve or expect."
Obama is known for drawing huge crowds to many of his speeches. In May, a record 75,000 jammed into a riverside park in Portland, Ore., to hear him speak shortly before that state's primary. His convention speech on the final night of the convention coincides with the 45th anniversary of Martin Luther King Jr.'s "I Have a Dream" speech on the steps of the Lincoln Memorial in 1963.
The Illinois senator is running to be the first black president.
