Porcello, who turns 31 on Dec. 27, had multiyear offers but preferred a one-year deal, according to reports.
A ground ball pitcher who relies on a sinking, two-seam fastball, Porcello is coming off a career-worst season with the Red Sox. He was 14-12 but had a 5.52 ERA that was the highest in the majors.
He has been quite durable over the past four seasons, making at least 32 starts per year, but the velocity on his slider dropped by 1.7 mph from 2018, which made the pitch far less effective. He gave up a troublesome .314/.407/.571 slash line with runners in scoring position in 2019.
He signed a four-year, $82.5 million contract extension with the Red Sox in 2015. In his five seasons with Boston, he had one great season -- winning the American League Cy Young Award in 2016, when he was also voted Comeback Player of the Year.
Porcello led the majors with 22 wins in 2016 and had career-bests in innings pitched (223), strikeouts (189), ERA (3.15) and WHIP (1.01). He allowed only 32 walks over the entire season and threw three complete games.
In 11 seasons with the Red Sox and Detroit Tigers, Porcello has a 149-118 record and a 4.36 ERA.
ESPN's Buster Olney and Keith Law contributed to this report.