Jon Heyman of the MLB Network reported it's a $3.1 million deal with a potential for $600,000 in incentives.
Renfroe is coming off a down year with the Tampa Bay Rays. He posted career lows in batting average (.156) and OPS (.645) while hitting eight home runs in 42 games during the coronavirus-shortened 2020 season.
The numbers represented a sharp decline from his previous three seasons with the San Diego Padres. He compiled a .777 OPS with 85 homers in 379 appearances for the Friars from 2017 through 2019. Last December the team traded him to Tampa in a deal that included Tommy Pham.
That form rarely materialized with the Rays as his struggles carried into the postseason, when he finished with a .687 OPS in 12 games during his first trip to the playoffs.
The 28-year-old Mississippi native will attempt to bounce back with the Red Sox in 2021.
Boston selected him in the 31st round of the 2010 MLB draft. He opted to honor his commitment to Mississippi State rather than go pro and, after a standout career with the Bulldogs, the Padres took him with the 13th overall pick in the 2013 draft.
Renfroe said Monday he'll reach out to Danny Watkins, a Red Sox area scout, after signing a decade following the club's initial effort.
"I'm very excited to be part of the Boston Red Sox," he told reporters. "Obviously, they were the first ones to take a shot at me in high school. They drafted me in high school in 2010. I'm pretty excited to get back and to sign with them, that's pretty exciting. I'm probably going to text Danny Watkins after this, and it took 10 years for me to sign with the Red Sox, but I finally did it. It's pretty cool and I'm very excited for it."
In addition, the slugger attributed his 2020 struggles to the unique nature of the campaign.
"As far as last year and what happened last year, it was an unprecedented season that's never been seen before in history," Renfroe said. "It was tough for everybody. People, players, coaches, family members, everybody, and I think not necessarily getting the amount of at-bats that everybody is used to and things like that. It was kind of an overwhelming experience for everybody."
Renfroe should open 2021 as Boston's starter in right field, but he could cede playing time to youngsters Yairo Munoz, Marcus Wilson or Jarren Duran if he gets off to another sluggish start. Alex Verdugo is projected to shift to center field with Jackie Bradley Jr. having headed to free agency.