Ron DeSantis will be the next Florida governor, extending Republican control of the state's highest office to a sixth straight four-year term and proving that a candidacy nearly entirely about President Donald Trump can win the top office in a major state.
Gillum would have been Florida's first black governor, and over two-thirds of voters said that it is important to elect more racial and ethnic minorities to public office.
DeSantis, who attended Yale University and Harvard Law School, resigned his seat in the U.S. House of Representatives in September to focus exclusively on his gubernatorial bid. Gillum, the current mayor of Tallahassee, has 50 percent of support among likely voters, versus 46 percent for his GOP rival.
But in Wisconsin, Democrat Tony Evers pulled off a narrow win in unseating Republican incumbent Scott Walker, according to data provider DDHQ.
"Earlier this evening I called Mr Ron DeSantis and congratulated him on what we expect will be him as the next governor of the great state of Florida".
As governor, DeSantis will essentially be Trump lite.
Trump-backed Rep. Ron DeSantis ran a tight race against Gillum, a Bernie Sanders-backed candidate and the mayor of Tallahassee, who secured an impressive victory in his August primary. FiveThirtyEight predictions had showed Gillum 4.2 percent ahead of DeSantis on Election Day.
He added that "people are going out and they're voting for something and not against".
Florida is the most populous of the battleground states that swing between the parties in presidential elections, but Republicans have controlled the governor's mansion for two decades. Additionally, his campaign cut ties with a volunteer during the final weeks of the race, after the volunteer was caught on video calling Florida a "cracker" state and saying the campaign was taking advantage of "white guilt".
In both the gubernatorial race and the Senate contest, voters concerned with health care and gun policy broke heavily for Democrats Gillum and Nelson.
In Oklahoma, Republican Kevin Stitt defeated Democrat Drew Edmondson, dashing Democratic hopes that outgoing Republican Governor Mary Fallin's low approval numbers had provided a rare opportunity in a deeply conservative state.
But Gillum, who is just 39, vowed to remain involved in politics.
He joked during brief remarks that he wasn't sure his wife, R. Jai Gillum, whom he met at Florida A&M University, had voted for him. Despite implications that DeSantis was racially insensitive - an idea he angrily disputed during a debate - he was able to win the state that Trump carried in 2016.