Walsh, a first-term member of Congress who is running in a new district following reapportionment, told an audience in Elk Grove Village, Ill., Sunday heroes tend not to talk publicly about their military service.
"That's what's so noble about our heroes," he said. "Now I'm running against a woman who, I mean, my God, that's all she talks about. Our true heroes, the men and women who served us, it's the last thing in the world they talk about."
Duckworth, a lieutenant colonel in the Illinois Army National Guard, was a Black Hawk helicopter pilot when she lost her legs and the use of an arm in combat in Iraq in 2004. Her campaign called Walsh's comment an insult "to those who sacrificed to make this country free," the Chicago Tribune reported Tuesday.
In an interview Tuesday with MSNBC, Duckworth said, "Anyone who has worn the uniform of this great nation for a single day has done more for their nation than Joe Walsh has ever done."
Walsh issued a statement Tuesday calling the controversy a "political ploy to distort my words and distract voters."
"Of course Tammy Duckworth is a hero," he said. "I have called her a hero hundreds of times."
VoteVets.org -- which lobbies for legislation that benefits troops and veterans and describes itself as non-partisan but progressive -- criticized Walsh's comment and said "all veterans are heroes."