FLORIDA — Tallahassee Mayor Andrew Gillum has won the Democratic primary in Florida's gubernatorial race in a surprise upset.

Gillum ultimately won by 34.2 percent of the vote, with former Congresswoman Gwen Graham narrowly behind at 31.4 percent of the vote. Former Miami Beach Mayor Philip Levine had 20.3 percent of the vote.

"There were just a few people who believed this would not be possible. And then there were a few more people who believed it was," Gillum said in his victory speech Tuesday night.

The Democratic primary was a crowded one. Seven candidates fought for for the Democratic gubernatorial ticket, with Gillum surpassing many expectations.

A St. Pete Polls survey released Monday showed Gwen Graham leading in the democratic race for Florida governor.

She had the endorsements of Orlando Mayor Buddy Dyer, Tampa Mayor Bob Buckhorn, and just Tuesday received the endorsement of Puerto Rico’s governor. 

But the same St. Pete Polls survey showed Gillum surging forward. He told Spectrum News he is expecting to “shock the political system.”

"I want you to know ... that this thing is not me, it never has been and it never will be. This race is about every last one of us," Gillum said when he accepted his nomination.

Gillum says he believed his campaign was built on timing — surging at the right time, especially with the recent endorsement of former presidential candidate Sen. Bernie Sanders.

"He knit together a constituency of the liberals and progressives that extended from the northwest corner of the panhandle, down to the southeast corner of the state, picking up Orange County in the middle and Hillsborough on the west," said Jay Leve, President of SurveyUSA, that polled for Spectrum News.

That, combined with young voter gathering, was not foreseen by many people.

"Gillum literally locked up that constituency, the far left constituency, and rolled right through the state with that as his tailwind," Leve said.

Meanwhile, Levine was among the candidates rallying supporters until the very end.

His campaign told Spectrum News their internal polling shows this will still be a neck-and-neck finish.

Levine says his momentum came from an expansive ground game, with 14 offices statewide and hundreds of volunteers.

When Graham conceded late Tuesday night, she promised Gillum that she would do all she could to help his campaign and help him win November's gubernatorial race.

Levine also expressed support for Gillum in a tweet Tuesday night.

Overall, Gillum's speech honed in on a cornerstone of his campaign -- his promise to fill the needs of "everyday" people.

"I sincerely believe that what is going to deliver us to victory in November is the fact that there are everyday, hardworking people in the state who believe that they deserve a voice in our government too, and we're gonna give it to them," Gillum said.

He also added, "What's going to bring us together is our common and sure belief that regardless of where you come from ... regardless of what side of the tracks you live on, that every single Floridian (ought to) have their fair and equal shot of the American dream."

More than 2 million voters cast their ballots ahead of the Aug. 28 primary election.

Gillum will face Republican gubernatorial candidate Ron DeSantis in November.

Reporters Greg Angel and Eric Levy contributed to this story.

Follow Election Night tweets and reporting live: