Giolito’s contract also includes a mutual option for 2027.
The 31-year-old spent last season with the Boston Red Sox, registering a 3.41 ERA and 1.29 WHIP over 26 starts.
In 206 career games also with the Washington Nationals, Chicago White Sox, Los Angeles Angels and Cleveland Guardians, Giolito owns a 4.30 ERA while striking out 9.3 opponents per nine innings.
San Diego was tied for the NL West lead at 16-7 entering action on Wednesday.