The deal includes a mutual option for 2026.
Jansen, who turns 30 in April, hit .205 with nine homers and 24 RBIs last season for Toronto and Boston, which acquired him from the Blue Jays in a July 27 trade.
He made headlines when he played for both teams in the same suspended game — a first in major league history. Jansen even batted for both clubs in the same inning of a rain-delayed contest he started for Toronto in June before it was completed in late August.
Jansen has a .220 batting average with 74 homers and 220 RBIs in seven major league seasons with Toronto (2018-24) and Boston.
