Rosenhaus said the deal includes $19.95 million fully guaranteed.
Flowers, who turns 26 on April 25, signed a one-year deal with Washington last offseason, hoping to revive a career that had stumbled. He did so by switching positions, moving from tackle to left guard.
The position switch suited him well, and he started every game in 2019. Flowers didn't become a Pro Bowler, but he did stabilize the position. His size -- 6-foot-6, 330 pounds -- and strength turned him into a good run-blocker inside, and he had a career-high 92% pass block win rate, according to ESPN Stats & Information. He had an 84% pass block win rate in 2018 and 83% win rate in 2017.
The Dolphins entered free agency with the NFL's most cap space at about $90 million. Adding offensive line help was a top priority after Miami tied for last in sacks allowed in 2019 with 58.
The Dolphins will still examine additions along the offensive line in free agency and the draft.
Flowers, a Miami native who went to the University of Miami, is likely to fill a starting guard spot for the Dolphins after returning home for a big payday.
"I'm excited to go to Miami. That is where I am from. I always wanted to be home. That's why I stayed home in college," Flowers told ESPN's Josina Anderson. "New York for me was just a learning experience. Everything after that has been great."
The New York Giants selected Flowers with the ninth pick in the 2015 draft and made him the immediate starter at left tackle. He played in 15 games as a rookie but struggled for most of his time in New York, due in large part to inconsistent technique.
In his fourth season, he started only two of the five games he played for the Giants, who released Flowers after failing to trade him. Three days later, the Jacksonville Jaguars signed Flowers, and he started seven of the final eight games. But the Jaguars let him hit free agency, and he eventually signed with the Redskins.
ESPN's John Keim contributed to this report.