Gillum, who was trying to become the state's first black governor, told a crowd gathered on the campus of Florida A&M University, "I sincerely regret I couldn't bring it home for you".
Florida's term-limited governor won a narrow victory for a U.S. Senate seat, flipping yet another seat to the GOP.
Voters in Florida have a rare clear choice between a rock-solid conservative and a democratic socialist for governor. DeSantis offered few specifics on how he would govern Florida, other than to say he would continue the economic policies of current GOP Gov. Rick Scott with low taxes and few regulations. Gillum, a liberal Democrat, and DeSantis, who has tried to imitate Trump in every way, provided voters with a pretty intense contrast.
Republican candidate for Florida governor Ron DeSantis speaks during an event put on by the Police Benevolent Association in Palm Beach County, on October 3, 2018.
Both DeSantis and Scott were projected to lose in the days leading up to the election, according to numerous polls.
With more than 99 percent reporting, DeSantis had a more than 77,000-vote lead out of 7.9 million ballots reported.
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.
But the Democrats were trailing in redder areas of the state. "We recognize that we didn't win this tonight". And just because we didn't always come out victorious we didn't retreat.
While much of the elections' focus was on which party would win control of the US Congress, Republicans and Democrats were battling across the country for state-level power.
Gillum received more than 10,200 votes than Nelson, while DeSantis received more than 10,000 votes than Scott.
The gubernatorial race was a study in contrasts: a straight-talking, unapologetically progressive, black nominee running against a Tea Party figure who released a campaign ad in which his young children built Trump's fabled border wall out of toy bricks.
Republicans controlled 33 governors' mansions and two-thirds of state legislative chambers going into Tuesday. County-level results showed Mucarsel-Powell won enough ballots in Miami-Dade to overcome Curbelo's advantage in the Keys.
In Colorado, Democrat Jared Polis was set to become the first openly gay man to be elected governor of a USA state, after NBC News projected him to win against Republican Walker Stapleton.