She ended speculation that she would quit the race on Fox News' "Hannity & Colmes" political talk show. Rumors swirled that she would withdraw after her name was associated with a defense contractor who bribed another congressman.
"I'm staying. I'm in this race. I'm going to win," she said. "I'm going to put everything on the line."
Harris, a citrus and cattle heiress, has been under mounting pressure from Republicans to get out of the race because of concerns that she cannot win and that her role as Florida's secretary of state during the 2000 presidential recount could drive Democrats and independents to the polls in droves.
A University of North Florida poll released hours before her television appearance showed Harris 20 points percentage points behind opponent Bill Nelson, 48 percent to 28 percent. The statewide poll of 591 registered voters has a margin of error of plus or minus 4 percent.
Her campaign has had difficulties since last summer. GOP leaders in Washington sought a primary opponent for her, believing her role in securing President Bush's 537-vote victory would galvanize Democrats and independents against her.
The lack of party support led to lower-than-expected campaign contributions. Harris began the year trailing Nelson in fundraising, $8 million to $1 million.
Her campaign became more difficult after a defense contractor involved in a bribery scandal said he also gave Harris illegal campaign contributions.
Mitchell Wade, the former president of MZM Inc., admitted making $32,000 in illegal contributions to Harris' 2004 campaign for the House. Wade also pleaded guilty to bribing former U.S. Rep. Randy "Duke" Cunningham, R-Calif., who was sent to prison earlier this month for bribery.
Harris said she did not knowingly do anything illegal and said she would donate the money to charity.