Halvorson first ran for the Illinois State Senate in November 1996, defeating incumbent Republican State Senator Aldo DeAngelis 56%–44% in Illinois' 40th Senate District.[5][6] In 1998, she won re-election to a second term defeating State Representative Flora Ciarlo 66%–34%.[7] In 2002, she won re-election to a third term unopposed.[8] In 2006, she won re-election to a fourth term with 70% of the vote.[9]
After being diagnosed as a high risk for cervical cancer due to HPV, Halvorson gained special notoriety and controversy by creating a program intended to broaden access to HPV testing and vaccination.[10]
Following Halvorson's election to the House, there was an ongoing process, narrowed to three possible candidates, for Halvorson's successor in the Illinois Senate; she was eventually replaced by Toi Hutchinson. Just before Halvorson was set to officially resign from her seat, GovernorRod Blagojevich was arrested. Halvorson said, "As frustrated and disappointed as I was, I was not surprised."[13] She also called for Blagojevich to resign.[14]
In September 2007, incumbent Republican U.S. Congressman Jerry Weller announced that he would not seek another term, citing the need to spend more time with his family. Halvorson won the open seat against Republican businessman Marty Ozinga with 58% of the vote, while Ozinga only got 34%. In 2020, Ozinga's son, Tim Ozinga, was elected to the Illinois House of Representatives.
Halvorson lost to Republican nominee Adam Kinzinger 58%–42%. Despite her landslide victory two years earlier, this was the fifth-largest margin of defeat for a Democratic house incumbent in 2010.
In September 2011, Halvorson filed a candidacy with the FEC to run in the newly redistricted Illinois's 2nd congressional district, against incumbent Democrat Jesse Jackson, Jr. “He (Jackson) lives in D.C. He doesn’t come home on weekends. His kids go to school in D.C."[17] She also said that “They should be fearing me becoming a congresswoman. I represent the people who live in the (current) 11th district. He’s just nervous that I’m going to become a congresswoman because then his control is over.”[18] The newly drawn district is just 54% African American.[19] Jackson defeated her 71%–29%.
On November 21, 2012, Jesse Jackson Jr. resigned from office.[20] Halvorson announced her candidacy on November 26 [21] but lost the primary election on February 26, 2013.[22]
On October 2, 2007, Halvorson announced her decision to run for Illinois's 11th congressional district in the United States House of Representatives, after current incumbent Jerry Weller announced in September that he would not be running for re-election. EMILY's List endorsed Halvorson in November. In February 2008, Republican nominee, New Lenox Mayor Tim Baldermann, withdrew from the race, citing other obligations.[23] He was replaced by Marty Ozinga, whom Halvorson easily defeated in the general election.
Halvorson was appointed to the powerful Steering and Policy Committee as well as a member of Veterans, Small Business and Agriculture. One of her true loves is Economic Development and Transportation. During her time in office she said that one of her main focuses were constituent services.[24] She has agreed with the 2009 Economic Stimulus Act, Cap and Trade of Emissions, and the Federal Health Care Bill.
