Whitmire, 74, who is one of Texas' most powerful Democratic legislators, will now be at the helm of America's fourth-largest city.
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"We ran a very positive campaign," Whitmire told ABC13's Brooke Taylor shortly before his acceptance speech. "Houston is a great city - it's a special city, and we're demonstrating it tonight."
His campaign focused on reducing crime, improving streets and bringing people together. He heavily outspent Jackson Lee, who was running to become Houston's first Black female mayor.
"We're going to have a safer city, we're going to quit kicking our problems down the road," Whitmire said. "We're not New York or Chicago or LA. We're Houston. We fix our problems."
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The congresswoman's campaign also had to deal with fallout from the release in October of an unverified audio recording that allegedly captured her profanely berating staff.
Whitmire and Jackson Lee made it to Saturday's runoff after emerging from a crowded field of nearly 20 candidates in the Nov. 7 general election.
Both candidates - two of Houston's biggest political fixtures - touted their decades-long political experience as strong qualifications to lead a growing city, which faces a variety of challenges, including crime, crumbling infrastructure and potential budget shortfalls.
SEE ALSO: Whitmire commits to keeping HPD Chief Finner during final mayoral debate
Whitmire started in the Texas Legislature in 1973, first as a state representative and the majority of his time as a state senator. Jackson Lee has represented Houston in Congress since 1995 and before that had served on Houston's City Council.
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Booming growth over the last decade has caused municipal headaches, but has also turned the Houston area into an expanding stronghold for Texas Democrats. Although the mayoral race is nonpartisan, Whitmire and Jackson Lee are both Democrats.
Whitmire will be the oldest big city mayor in the U.S. He is set to lead a city which is becoming younger, with a median age of around 35 and with 25% of its population below 18, according to census figures.
The choice between Whitmire and Jackson Lee, who is 73, frustrated some Democratic voters, particularly younger ones, at a time when the party is searching for new political stars in Texas who might end 30 years of GOP dominance statewide.
The new mayor will have to deal with new laws from the GOP-led state government over control of local elections and the ability to impose local regulations.
Whitmire will replace Mayor Sylvester Turner, who has served eight years and can't run again because of term limits.
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Whitmire will also lead what is considered one of the country's most diverse cities. Of the city's 2.3 million residents, 45% are Latino, with 23% Black and 24% white. One in every four Houston residents was born outside the U.S.
Known as the energy capital of the world, Houston's economy has long been tied mainly to the oil industry. But the city is working to become a leader in the transition to cleaner energy. Like other large U.S. cities, Houston is also dealing with a lack of affordable housing and concerns among residents over growing gaps between the rich and poor.
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