Shane Missler matched five numbers and a bonus ball to scoop the fourth largest win in the US game's history.
He opted to receive a one-time payment of $282m, instead of the full amount over a longer period of time.
Mr Missler said he had a feeling he could win on the night of the Mega Millions draw, says a press release.
Minutes after the draw a week ago he posted on Facebook: "Oh. My. God."
Mr Missler presented his winning ticket at the state lottery headquarters in Tallahassee on Friday, accompanied by his father and a lawyer.
He said he has big plans for his winnings.
"I'm only 20, but I hope to use it to pursue a variety of passions, help my family and do some good for humanity," said Mr Missler, according to the statement.
He told the Tampa Bay Times: "I intend to take care of my family, have some fun along the way and cement a path for financial success so that I can leave a legacy far into the future."
His lawyer said his client had "retired" from his job at a company that carried out employment background checks.
Mr Missler bought the winning ticket at a 7-Eleven in his hometown of Port Richey, 40 miles (64km) north of Tampa, using a "Quick Pick" option that selects the numbers randomly.
The winning numbers were 28, 30, 39, 59, and 70 with a "Mega Ball" of 10.
"If there is one thing I have learned thus far in my short time on this earth it is that those who maintain a positive mindset and stay true to themselves get rewarded," Mr Missler said.
"I look forward to the future."