With 123,967 ballots counted, Gallego had captured nearly 59 percent of votes, giving her a 17-point lead. That put her opponent, former city council member Daniel Valenzuela, at 41.33 percent. Valenzuela, a Glendale firefighter, would have been Phoenix's first Latino mayor.
Thronged by staffers and supporters at her victory party at Crescent Ballroom, Gallego cast her victory as a win for her values.
"We fought for inclusivity, we fought for innovation, we fought for a sustainable city, and the voters responded," she said to a full house.
Gallego took a moment to thank Valenzuela and give a nod to his supporters, saying, "I am going to be a mayor for everyone."
Still, she managed to sneak in a dig at outside "dark money" groups who smeared her as the election became more tense this month. "We overcame doubters, rain," she said. "We overcame dark money and a lot of it."
Valenzuela conceded the race in a tweet, saying, "Tomorrow morning I will continue to serve you as a lifelong public servant. Congratulations to our next mayor, @KateWGallego."
Thank you, Phoenix. I appreciate all you’ve done for me. Tomorrow morning I will continue to serve you as a lifelong public servant. Congratulations to our next mayor, @KateWGallego. pic.twitter.com/1auks5NSc5— Daniel Valenzuela (@Daniel4PhxMayor) March 13, 2019
Just before Valenzuela conceded, at his watch party at Paz Cantina, supporters quietly checked their phones as the first results came in, because the screens that at first showed "0 votes" tallied and remained unrefreshed had been replaced with the bright, blue-and-white logo of "Daniel Valenzuela for Mayor." The supporters asked others around them if they'd seen the results, then exchanged knowing looks.
"I'm proud of the race we ran," Valenzuela said after his concession. He said his campaign didn't succumb to political attacks, but focused on the issues.
"While tonight did not bring the result that ... we had hoped for ... I congratulate Kate Gallego on her victory tonight," he said.
Gallego will replace interim Mayor Thelda Williams, who was appointed to the seat in May after former mayor Greg Stanton resigned to run his successful campaign for Congress. Gallego came in first during a November election for mayor by a wide margin, but did not get the 50 percent of votes required to avoid a runoff with Valenzuela, the runner-up.
Gallego is scheduled to be sworn in as mayor on March 21. Her term is slated to end in 2021.
Before running for elected office, Gallego worked on strategic planning and economic development for the Salt River Project. In 2016, she divorced her ex-husband, U.S. Congressman Ruben Gallego, with whom she has a son.
She received the backing of progressives, labor unions, the Arizona Republic's editorial board, and liberal advocacy organizations like Emily's List, Sierra Club, and the Planned Parenthood Advocates of Arizona.
Although both mayoral candidates are Democrats, conservatives coalesced around Valenzuela. He also had the backing of several labor unions, Arizona Police Association, and the Greater Phoenix Chamber of Commerce.
Both candidates raised millions of dollars and benefited from support from independent expenditure groups.
Gallego and Valenzuela had quarreled over minor policy disagreements since the summer, but the race took a heated and ugly turn in the final stretch of weeks.
Advancing Freedom Inc, an Oklahoma-based nonprofit, sent mailers attacking Gallego for serving as a Hillary Clinton super-delegate and labeling Valenzuela as the "conservative choice." The same group also took out ads on Breitbart, the far-right news site.
Valenzuela defended himself by saying his campaign does not coordinate with groups spending "dark money" to support him, but he still came under fire for not denouncing them.
An independent group called Bringing Arizona to Action attacked Valenzuela, sending fliers with his face covered and blood, claiming he took "blood money from anti-immigrant hate groups." The hit was a reference to the Arizona Police Association.
Gallego said she did not coordinate with Bringing Arizona to Action.
In addition to the mayor's race, Phoenix held two city council elections to replace Valenzuela and Gallego.
At press time, both races appeared too close to call.
Betty Guardado led the race for District 5, with 23.76 percent of the votes. Interim council member Vania Guevara and Audrey Bell-Jenkins had 25.08 percent and 23.76 percent of votes, respectively. Lydia Hernández trailed with 15.38 percent. Valenzuela held the seat from 2012 to 2018
Carlos Garcia was leading the District 8 race with 28.49 percent. He was followed by Mike Johnson and Lawrence Robinson, who had 22.36 and 20.26 percent, respectively. The rest of the candidates were out of contention.
If no candidates in the city council races get 50 percent of the vote, the top two vote-getters in each race will be headed for a runoff election on April 22.
New Times writer Elizabeth Whitman contributed to this article.
Correction: Gallego isn't the first mother to lead the city — former Mayor Margaret Hance and her husband had three children.