Instead of taking the full prize across several payments over a period of time, the Florida resident opted to receive a one-time payment of almost $282m (£205m).
Lottery officials said the win came after the man, from Port Richey, had five winning numbers and a "mega ball" number drawn on 5 January.
Florida Lottery said it was the fourth largest Mega Millions win in history.
Since his win, Mr Missler posted a photo of a book by businessman Gary Vaynerchuk he appeared to be reading, and added: "Young entrepreneur in the making."
He later tweeted: "The power of positive thinking should not be underestimated!"
The winner told Lottery organisers he believed in the power of a positive mindset and that he was not surprised he had won. He said he had "a feeling" that he might.
The power of positive thinking should not be underestimated!— Shane Missler (@TheShaneMissler) January 11, 2018
His brother was the first person he called after receiving the news. He later told his father the following morning over a coffee.
Mr Missler said: "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."
The man, who worked as a verification specialist at a background screening firm - according to his Facebook - told the Tampa Bay Times he was going to "take care" of his family.
Source : https://news.sky.com/story/florida-man-shane-missler-20-who-won-451m-jackpot-to-do-good-for-humanity-11205320