As an attorney at Mayer Brown, Lightfoot represented Republicans in two cases protesting Democratic gerrymandering. At Mayer Brown, she also defended Chicago police officer Paul Powers against charges of physical assault. In 2019, after facing criticism over defending Powers, Lightfoot cited video evidence in favor of her former client's innocence.
Lightfoot won the runoff election on April 2, 2019, becoming mayor-elect of Chicago. She won more than 73% of the overall vote in the runoff, winning in all 50 wards of the city. Lightfoot won all but 20 of the city's 2,069 voting precincts. Voter turnout was 32.89%, almost a record low.
Lightfoot took office on May 20, 2019. Incumbent mayor Rahm Emanuel reportedly modeled the transition between his and Lightfoot's administrations on the U.S. presidential transition between the George W. Bush and Barack Obama administrations. Emanuel was part of the Bush-Obama transition as Obama's Chief of Staff designate. Lightfoot endorsed the comparison between her transition and the Bush-Obama transition.
On April 6, 2019, Lightfoot told the Chicago Sun-Times that her staff would, during her first post-election weekend, spend time examining the city's 600-page agreement with Sterling Bay regarding the Lincoln Yards development. During her campaign, Lightfoot had been critical of the process that was being taken to reach the agreement. The following Monday, at her request, Mayor Rahm Emanuel postponed City Council votes on the approval of $1.6 billion in tax increment financing subsidies for both the Lincoln Yards and The 78 mega-developments. After the developers of the two projects agreed to increase commitments to hiring minority-owned and women-owned contractors, Lightfoot announced that she now supported the deals, which were approved one day subsequent to her declaration of support.
On May 20, 2019, Lightfoot officially took office as Mayor of Chicago, after being sworn in at 11:15 am by Magistrate Judge Susan E. Cox of the U.S. District Court for the Northern District of Illinois, at the Wintrust Arena, accompanied by her wife and daughter.
On October 14, 2019, Lightfoot announced the creation of an affordable housing task force set to consist of 20 members and study solutions to housing affordability over a 4 to 6 month period. The following month, it would be announced that the task force would also come up with a proposal to rewrite the city's affordable housing ordinance.
On May 28, 2019 Lightfoot unveiled proposals to revise the operating rules of the Chicago City Council. Among other things she proposed live streaming video of committee meetings, changes to strengthen the rule on conflicts of interest and the transfer of control over TIF subsidies to the Council's Committee on Economic and Capital Development.
Lightfoot has butted heads with embattled Alderman Ed Burke. On May 29, 2019, during the first City Council meeting, over which Lightfoot presided, she held her ground in debating issues with Alderman Burke. On May 31, after indictments were brought against Burke, Lightfoot called for his resignation.
On June 5, 2019, Lightfoot outlined further ethics reform proposals for the City Council.
On June 3, 2019, Lightfoot announced her selections for the Chicago Public Schools school board, appointing former City Clerk of Chicago Miguel del Valle as its president. She also announced that incumbent Chicago Public Schools CEO Janice Jackson would retain her position, having previously only committed to retaining her for an interim period.
In October 2019, Lightfoot dealt with a public schools strike led by the Chicago Teachers Union and Service Employees International Union.
On May 28, 2019 Lightfoot outlined plans to remedy the city's fines and fees programs, increase its minimum wage to $15 an hour by 2021.
On November 26, 2019, the Chicago City Council approved Lightfoot's budget for the 2020 fiscal year.
On May 28, 2019, Lightfoot outlined a plan to focus on reducing the city's gun violence.
On May 28, 2019, Lightfoot urged City Council to pass an ordinance within her first hundred days that would establish a level of civilian oversight on the Chicago Police Department.
Lightfoot launched a community policing initiative in June 2019. Later that month she announced that the city's police department would not assist U.S. Immigration and Customs Enforcement (ICE) raids, denying ICE access to the city's police database in an effort to protect the city's immigrant population from the threat of deportation.
On November 8, 2019, after Eddie T. Johnson announced that he would resign from his position as Superintendent of the Chicago Police Department, Lightfoot named Charlie Beck to serve as interim Superintendent of the Chicago Police Department. On December 2, rather than letting Johnson voluntarily retire, Lightfoot fired him due to what she declared were "intolerable" actions by him and him misleading the public. Lightfoot nominated David Brown to be Superintendent of Police on April 2, 2020. After Beck stepped down on April 15, Brown became acting Superintendent, while pending confirmation to serve on a permanent basis.
On November 13, 2019, Lightfoot proposed an ordinance that would create a new Office of Public Safety Administration, which would combine administrative functions of Chicago Police Department, the Chicago Fire Department and the Office of Public Safety Administration. The ordinance would also move the task of hearing appeals from rejected Chicago police applicants whose names have been removed from the department’s eligibility list from the Human Resources Board to the purview of the Chicago Police Board.
On May 20, 2019, Lightfoot announced the retention of several administrators who had worked under the previous Emanuel administration, alongside a number of new hires.
On June 3, 2019, Lightfoot announced her selections for the Chicago Public Schools school board, appointing former City Clerk of Chicago Miguel del Valle as its president. She also announced that incumbent Chicago Public Schools CEO Janice Jackson would retain her position, having previously only committed to retaining her for an interim period.
On September 30, 2019, Lightfoot hired former alderman John Arena as a special advisor in the city's planning department.
In November 2019, Lightfoot named Charlie Beck to serve as interim Superintendent of the Chicago Police Department. On December 2, 2019, rather than allowing Superintendent of the Chicago Police Department Eddie T. Johnson to voluntarily retire, as he had planned to do, Lightfoot fired him due to what she declared were "intolerable" actions by him and him misleading the public. Lightfoot nominated David Brown to be Superintendent of Police on April 2, 2020. After Beck stepped down on April 15, Brown became acting Superintendent, while pending confirmation to serve on a permanent basis.
In December 2019, Lightfoot nominated Gia Biagi to serve as the Commissioner of the Chicago Department of Transportation. Biagi was confirmed by the Chicago City Council to the position on January 15, 2020.
On May 28, 2019, Lightfoot laid out plans to pass "fair work week" legislation tightening rules surrounding workplace scheduling.
On November 26, 2019, the City Council approved ordinances Lightfoot had put forth placing restrictions on vehicle impoundment and lowering fines for illegal possession of cannabis.