He rose through the ranks and became Deputy Commissioner of Operations in 2000, succeeding the likes of Ed Norris and Jack Maple, who implemented COMPSTAT meetings.

McCarthy was in the middle of ground zero during the September 11 attacks, working closely with then-Mayor Rudy Giuliani to operate an emergency response command post.

[4] (During the 2020 Democratic Primary debates, Vice-President Biden nick-named McCarthy as "Giuliani's guy" in an attack towards Senator Booker.)

[13][14] On October 20, 2014, Laquan McDonald was murdered by Chicago Police Officer Jason Van Dyke.

[22] In April 2022, McCarthy was announced as the interim police chief of Willow Springs, Illinois, a town of 5,857 people near the Cook and DuPage county border.

McCarthy alluded to how more than a dozen others ran for the office when Emanuel announced he wouldn’t seek a third term.

[26] During his candidacy, when meeting with the Chicago Sun-Times editorial board unsuccessfully seeking their endorsement[27] (which ultimately went to Lori Lightfoot),[28] McCarthy made news for proposing, to address the issues of population loss and budgeting the city's pension obligations, that Chicago should annex nearby suburban communities such as Evergreen Park, Norridge, Oak Lawn and Oak Park.