CHICAGO - Paul Vallas and Brandon Johnson will meet in a runoff to be the next mayor of Chicago after voters denied incumbent Lori Lightfoot a second term, issuing a rebuke to a leader who made history as head of the nation’s third largest city.

Mr. Vallas, a former schools CEO backed by the police union, and Johnson, a Cook County commissioner endorsed by the Chicago Teachers Union, advanced to the April 4 runoff after none of the nine candidates was able to secure more than 50 percent of the vote on Tuesday to win outright.

Ms. Lightfoot, the first Black woman and first openly gay person to lead the city, won her first term in 2019 after promising to end decades of corruption and backroom dealing at City Hall. But opponents blamed Ms. Lightfoot for an increase in crime that occured in cities across the U.S. during the pandemic and criticized her as being a divisive, overly contentious leader.

She is the first elected Chicago mayor to lose a re-election bid since 1983, when Jane Byrne, the city’s first female mayor, lost her Democratic primary.

Speaking to supporters Tuesday night, Ms. Lightfoot called being Chicago’s mayor “the honor of a lifetime.”

“Regardless of tonight’s outcome, we fought the right fights and we put this city on a better path,” Ms. Lightfoot said. She told her fellow mayors around the country not to fear being bold.

At his victory party, Mr. Vallas noted that Ms. Lightfoot had called to congratulate him and asked the crowd to give her a round of applause. In a nod to his campaign promise to combat crime, he said that, if elected, he would work to address public safety issues.

“We will have a safe Chicago. We will make Chicago the safest city in America,” Mr. Vallas said.

Mr. Johnson on Tuesday night noted the improbability that he would make the runoff, considering his low name recognition at the start of the race.

“A few months ago they said they didn’t know who I was. Well, if you didn’t know, now you know,” Mr. Johnson said. He thanked the unions that supported him and gave a special shout-out to his wife, telling the crowd, “Chicago, a Black woman will still be in charge.”

Ms. Lightfoot’s loss is unusual for mayors in large cities, who have tended to win re-election with relative ease. But it’s also a sign of the turmoil in U.S. cities following the COVID-19 pandemic, with its economic fallout and spikes in violent crime in many places.

There are clear contrasts between Mr. Vallas and Mr. Johnson.

Mr. Vallas served as an adviser to the Fraternal Order of Police during its negotiations with Ms. Lightfoot’s administration. He has called for adding hundreds of police officers to patrol the city, saying crime is out of control and morale among officers sunk to a new low during Ms. Lightfoot’s tenure.

Mr. Johnson received about $1 million from the Chicago Teachers Union for his campaign and had support from several other progressive organizations, including United Working Families. The former teacher and union organizer has argued that the answer to addressing crime is not more money for police but more investment in mental health care, education, jobs and affordable housing, and he was accused

by rivals such as Ms. Lightfoot of wanting to defund the police.

Crime was an issue that resonated with voters.

Rita DiPietro, who lives downtown, said she supported Ms. Lightfoot in 2019. But she voted for Mr. Vallas on Tuesday, saying she was impressed by his detailed strategy to address public safety.

“The candidates all talk about what they’d like to do,” she said. “This guy actually has a plan. He knows how he’s going to do it.”

Race also was a factor as candidates courted votes in the highly segregated city, which is closely divided in popula- tion among Black, Hispanic and white residents. Mr. Vallas was the only white candidate in the field. Ms. Lightfoot, Mr. Johnson and five other candidates are Black, though Ms. Lightfoot argued she was the only Black candidate who could win. U.S. Rep. Jesus “Chuy” Garcia was the only Latino in the race.

Ms. Lightfoot accused Mr. Vallas of us- ing “the ultimate dog whistle” by saying his campaign is about “taking back our city,” and of cozying up to the president of the Fraternal Order of Police, whom she calls a racist. A recent Chicago Tribune story also found Mr. Vallas’ Twitter account had liked racist tweets and tweets that mocked Ms. Lightfoot’s appearance and referred to her as masculine.