Duckworth declared herself the winner of Tuesday's primary after Raja Krishnamoorthi called to concede.
Duckworth will run against outspoken Republican Congressman Joe Walsh.
"He and I are very different," Duckworth said of Walsh. "While he is extreme, I'm practical. While he believes in raising his voice and ratcheting up the rhetoric, I believe in rolling up my sleeves and getting to work. While he believes our country needs a cultural war, I believe our country needs to come together to meet challenges."
The Democratic primary in 8th Congressional District, which spans several northwest suburbs, was aggressive. Both candidates raised more than $1 million during the campaign season.
But Duckworth had backing from the Democratic establishment, including an endorsement from U.S. Sen. Dick Durbin. She was most recently the former Assistant Secretary of Veterans Affairs in the Obama administration. She made an unsuccessful congressional bid in 2006 in another district.
Krishnamoorthi is a lawyer and engineer who runs a research and development firm in Bolingbrook.
"A few minutes I called Tammy and offered her congratulations on a very well-fought, clean fight," Krishnamoorthi said Tuesday night. "And she's an American hero, and she will get my full support in the fall election to battle against Joe Walsh."
The Associated Press contributed to this report.