Reliever Alex Torres heads to San Diego as part of the return package, along with right-handed pitcher Jesse Hahn.
In addition to Forsythe, the Rays also get infielder Maxx Tissenbaum and pitchers Matt Andriese, Brad Boxberger and Matt Lollis.
Forsythe, age 27, is coming off a 2013 season in which he batted .214/.281/.332 with six home runs in 75 games. For his career, he's a .241/.310/.349 hitter (88 OPS+) across parts of three major-league seasons. As well, Forsythe is capable manning shortstop, second, third and the outfield corners.
Tissenbaum, 22, hit .277/.365/.359 with 28 doubles, two homers, 49 RBI, 48 runs and four stolen bases for Class-A Fort Wayne in 2013.
Andriese, 24, was 11-7 with a 3.27 ERA, 1.22 WHIP and 105 strikeouts in 134 2/3 innings across Double-A and Triple-A last season.
Boxberger, 25, appeared in 18 games in relief for the Padres last season. He had a 2.86 ERA (121 ERA+), 1.46 WHIP and 24 strikeouts in 22 innings.
Lollis is a 6-foot-9 right-hander. The 23 year old went 3-8 with a 4.62 ERA, 1.69 WHIP and 63 strikeouts in 74 innings between High-A, Double-A and Triple-A in 2013.
As for Torres, the Padres are getting a 26-year-old lefty who last season pitched to a 1.71 ERA with 62 strikeouts and 19 unintentional walks in 58 innings of work. In parts of two MLB seasons, Torres boasts an ERA+ of 201 and an opponents' batting line of .172/.269/.233.
Hahn, 24, was 2-1 with a 2.15 ERA, 1.09 WHIP and 63 strikeouts in 67 innings for High-A Charlotte last season.