He played in Major League Baseball (MLB) for the San Diego Padres, Tampa Bay Rays, Los Angeles Dodgers, Minnesota Twins, Texas Rangers and Miami Marlins.

[3] He became the team's starting third baseman as a Sophomore[1] and improved to hit .347 in 61 games with nine home runs, 55 RBI and 18 stolen bases.

[3] He began his career that season in the low minors, appearing in nine games for the Arizona League Padres and three for the Eugene Emeralds.

[8] Forsythe began 2009 with the Lake Elsinore Storm of the California League[9] where he hit .322 in 66 games[8] and was named to the mid-season All-Star Team.

[8] In 2010, Forsythe was switched to second base[11] and played the entire season for the Missions, hitting .253 in 107 games with 38 RBI and 17 steals.

[14] Forsythe was optioned and recalled three more times during the summer of 2011[10] and recorded his first MLB hit on May 28, a single to left field of Henry Rodríguez of the Washington Nationals.

[18] His first major league home run was a walk-off on June 5 off of Steve Edlefsen of the San Francisco Giants.

[20] After a brief rehab stint with Triple-A Tucson, he was activated on June 10 when Jedd Gyorko went to the DL with a groin strain.

[21] Forsythe manned second base until Gyorko returned in mid-July, and then served the club in a utility role playing shortstop, second, and third as well as both corner outfield positions.

[7] On January 23, 2017, the Rays traded Forsythe to the Los Angeles Dodgers in exchange for José De León.

On July 31, 2018, Forsythe was traded to the Minnesota Twins, along with minor leaguers Devin Smeltzer and Luke Raley, for Brian Dozier.

[32] In the second half of the season with the Minnesota Twins, Forsythe appeared in 50 games batting .258 with no home runs and 14 RBIs.

On February 26, 2019, the Texas Rangers signed Forsythe to a minor league deal with a non-roster invitation to spring training.

[33] On March 22, 2019, the Texas Rangers announced that Forsythe had made the opening day roster as their utility infielder.

Forsythe appeared in 12 games for the Marlins, slashing .118/.211/.235[36] before being placed on the 60-day injured list with a right oblique strain and missing the remainder of the season.

[37] On May 4, 2021, Forsythe signed a minor league contract with the Milwaukee Brewers organization and was assigned to the Triple-A Nashville Sounds.