The deal is worth $54.125 million, with $26.8 million guaranteed, sources told ESPN, making Marpet one of the highest-paid left guards in the league.
Marpet took to Instagram on Tuesday evening to react to the extension.
View this post on Instagram
Today was a good day. So many people to thank including the Glazer family, Jason Licht, my coaches and teammates, and all of those who work at One Buc. Beyond excited to call Tampa Bay home and a huge shoutout to all the fans, my family and friends, Hobart College, and the village of Hastings. Stay in school, eat lots of tacos, work hard, and stay humble. #BucsNation #D3Nation #HOHNation
Marpet is among a handful of key players in the final year of their rookie contracts, along with left tackle Donovan Smith and middle linebacker Kwon Alexander, whom the Bucs have been trying to re-sign.
Smith tweeted congratulations to his teammate:
AALLLLIIIIIIIIIIII!!!!!!!!!!!! 💪🏾💪🏾💪🏾💪🏾 https://t.co/qJY6Sor3GE— Donovan Smith (@DSmith_76) October 9, 2018
Alexander also tweeted congratulations to Marpet.
A second-round draft pick out of Division III Hobart College, Marpet became a day one starter at right guard. He shifted to center and then left guard, starting 44 games over the past 3¼ seasons.
The Bucs became enamored with Marpet at the Senior Bowl, which prompted them to make him the first Division III player selected in the second round of the NFL draft.
Marpet has drawn praise from the Bucs' brass for his physicality, versatility, consistency, intelligence and communication skills. He has served as a captain, and he and Smith even assisted in the recruiting of center Ryan Jensen as a free agent.
ESPN's Adam Schefter contributed to this report.