The landslide victory makes Lightfoot the city's first black woman and the first openly gay person elected mayor.
"Today, you did more than make history," said Lightfoot during her acceptance speech. "You created a movement for change. When we started this journey 11 months ago, nobody gave us much of a chance. We were up against powerful interests, a powerful machine and a powerful mayor. But I remembered something Martin Luther King said when I was very young. 'Faith,' he said, 'is taking the first step even when you can't see the whole staircase.'"
Lightfoot, who will be sworn in on May 20th, succeeds Mayor Rahm Emanuel, whose popularity dropped significantly in the past several years. In September, Emanuel announced that he would not seek a third term.
In February, Lightfoot and Preckwinkle, Cook County board president and chair of the county's Democratic Party, received the most votes of the record-breaking 14 candidates in the mayoral race, but neither received the majority needed to avoid a runoff.
Lightfoot, 56, was a fresh face in Chicago politics, something she emphasized. "What we have heard from people is that they are really, really sick and tired of the same old, same old and want to break away from the past and I think that they view me as a change candidate, so I'm excited about that," said Lightfoot during her campaign.
The attorney ran on a platform that included ending corruption in city politics, police reform and investing in neighborhoods on the West and South Sides of Chicago.
Despite never having held elected office, Lightfoot brings significant experience including having worked with Chicago city government on police reform. Lightfoot served as an assistant United States attorney in the criminal division, president of the Chicago Police Board and chair of Chicago's Police Accountability Task Force. She has also held board positions at several progressive organizations such as ACLU Illinois and NARAL Illinois.
Most recently, Lightfoot was a the senior partner at law firm Mayer Brown.
Lightfoot, the granddaughter of a sharecropper from Arkansas, was born and raised in Ohio. Her mother worked as a home health aide and her father worked several jobs, including as a janitor, barber and handyman.
The mayor-elect attend the University of Michigan, where she graduated with honors, and earned a full scholarship to the University of Chicago Law School, where she served as the president of the Law Students Association and was the quarterback of the law school's intramural women's football team.
She has lived in Chicago since 1986 and today lives with her spouse, Amy Eshleman, on the near northwest side with their 10-year-old daughter.
"Out there tonight a lot of little girls and boys are watching. They're watching us. And they're seeing the beginning of something, well, a little different," said Lightfoot during her acceptance speech Tuesday. "They're seeing a city reborn, a city where it doesn't matter what color you are, where it sure doesn't matter how tall you are, where it doesn't matter who you love, just as long as you love with all your heart.
"In the Chicago we will build together, we will celebrate our differences. We will embrace our uniqueness. And we will make certain that we all have every opportunity to succeed. Every child out there should know this: Each of you, one day, can be the Mayor of Chicago."
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