She served one term in the United States House of Representatives, winning an at-large seat in Illinois in 1928.

She gave up the chance to run for re-election to seek a United States Senate seat from Illinois.

A decade later, she became the first woman to manage a presidential campaign, although her candidate, Thomas E. Dewey, failed to capture his party's nomination.

She was the daughter of Mark Hanna, a Senator and politician who was instrumental in the election of President William McKinley.

McCormick was instrumental in passing a partial suffrage law in Illinois in 1913, allowing women to vote in municipal and Presidential elections.

McCormick had the fame, the background and the determination to build a career on the new opportunities for women in high level politics.

As a spokesperson for the suffrage and for the Republican party, she made political activism attractive for partisan women.

[5][6] Their stops included Dakota where Hanna stepped in to give a speech for her ill father,[5] and Thomasville, Georgia, where she met her future husband Joseph "Medill" McCormick.

[3] A practical joke she played on the McKinleys, in which she pretended to have killed a wildcat on her own, led to reports that Hanna was an avid hunter.

[8] After high school, Hanna went to Washington, D.C., to work as a secretary for her father who was serving as United States Senator from Ohio.

[11]: 190 [12] In spite of their personal wealth, the couple lived at the University of Chicago Settlement, which introduced McCormick to many working women and helped her to understand the problems they faced.

[4] During their time living in Chicago, McCormick owned a dairy farm to provide untainted milk to locals, as part of the pure foods movement.

[4][13] She had long supported Progressive Party leader Theodore Roosevelt and found the switch to be consistent with the principles of her father, even though he had been a staunch Republican.

[15] McCormick worked closely with Grace Wilbur Trout to enact partial equal suffrage legislation in Illinois,[15] which gave women the right to vote in municipal and presidential elections.

[15] McCormick adapted techniques she learned from her father to devise a campaign to pressure every member of the legislature.

[15] Governor Edward F. Dunne signed the equal suffrage bill into law on June 26, 1913, gifting McCormick with one of the pens used in the signature.

[6] During her time as leader of the Congressional Committee, McCormick and Lewis J. Selznick of the World Film Corporation produced the melodrama Your Girl and Mine, which was intended to help gain support for the suffrage movement.

[11]: 190–91  As chair of the campaign committee, McCormick donated a gold elephant to be melted down and sold to help finance suffrage efforts in several states.

The elephant had been a gift from members of the Republican National Committee (RNC) to thank McCormick for traveling the country as part of the McKinley campaign.

[31] Two months after Medill's passing, McCormick threw herself into working at the Woman's World's Fair as general executive[32] and as a member of the event's Board of Directors.

[32] McCormick was convinced her husband had lost the primary due to the lack of engagement of Republican women voters.

[6] McCormick used that newly mobilized voting base when, in 1928, she ran in a heavily contested primary race for one of Illinois's at-large congressional seats.

[1] In the April 1928 primary election, she finished in first place in a field of eight candidates, including two sitting Congressmen, to win one of the two Republican nominations.

[b][37] By the time she entered Congress, McCormick had built a reputation as an astute politician for her years of working with her husband, and her ability to navigate the factions of Illinois politics.

[39]: 86 In September 1929, McCormick announced her intention to run for the Senate against Republican incumbent Charles S. Deneen, who had won the seat from her husband in 1924.

[40] By October, McCormick had returned to Illinois, visiting the state's various counties to rally support while Deneen was stuck in Washington, D.C., on Senate business.

[44] McCormick later testified that the campaign cost $252,572 of her own money (equivalent to $4,754,089 in 2024), with additional funds being raised from relatives.

[52][53] McCormick hired John Gaw Meem to add to the existing ranch house on the property,[52] and later to build the La Quinta Cultural Center which included a library, ballroom, art gallery, and swimming pool.

[63] Following the Dewey campaign's loss and the conversion of the Sandia Preparatory School into a military hospital, McCormick spent most of her time in Colorado,[5][18] where she focused on the operation of her ranch.

[66] The Rockford Chamber of Commerce posthumously named McCormick to its Northern Illinois Business Hall of Fame.