The contract is for $60 million and includes $34 million guaranteed, sources told ESPN's Adam Schefter.
Dawkins, who was entering the final year of his rookie contract, has been a mainstay at left tackle since he was picked in the second round of the 2017 draft. He hadn't been shy about his desire to stay in Buffalo.
"My main priority is to get better, and I know if I continue to grow and learn and get better, then all of the chips will eventually fall," Dawkins told ESPN in March. "As far as a new contract, I'm not worried about it. Whatever is supposed to happen is going to happen.
"I'm trying to be in Buffalo forever, so I've just got to do my part, and when the time comes, I'll be happy to sign on that dotted line."
Dawkins has started 43 games over the past three seasons and was a team captain in 2019, contributing as much to the team's culture as he has to its offensive line. He is the first player from the 2017 draft class -- the team's first under coach Sean McDermott -- to receive a contract extension.
Not only is Dawkins a valuable asset protecting third-year quarterback Josh Allen's blind side but he is also a threat as a receiver. He has recorded a receiving touchdown in each of the past two seasons, tying for the sixth most by an offensive lineman since 1970.
With this extension, Dawkins will overtake Arizona's D.J. Humphries as the NFL's fifth-highest-paid left tackle.
Dawkins, 26, had a down year in 2018 before bouncing back as one of the Bills' best players in 2019. His captaincy was a reflection of his self-realization over the offseason.
"At some point, it really all just clicked. I gained a deeper understanding of the game of football, the role I had to play and the way I had to play it," Dawkins said. "So many people look up to football players, and for the people who look up to me, I want to give them the best example of a full athlete that I can possibly give.
"It's OK to be the glue and the bridge to make people smile and to keep the energy during the down days as much as the good days."