Forsythe will begin the season at second base on Thursday when Double-A San Antonio opens the Texas League season.
Forsythe, a third baseman by trade, will likely remain at second base, alleviating the glut of third basemen in the system, according to Randy Smith, the Padres director of player development.
Forsythe played some second base in Spring Training and fared well there. Padres manager Bud Black said he liked Forsythe's actions at second base.
The move will allow the young infielder and fellow prospect James Darnell, also a third baseman, to play together on the field at the same time.
Smith said Forsythe will take ground balls before games with the Missions but that the move is, for now, permanent.
"We know what kind of third baseman he is, now we'll see how he looks at second base," Smith said. "At least we'll have that question answered."
Forsythe, 23, hit a combined .300 last season between Class A Lake Elsinore and with the Missions. Forsythe had 11 home runs, 61 RBIs and had a combined .429 on-base percentage.
Darnell, also 23, was the Padres Minor League position player of the year. He hit .311 in 126 games between Class A Fort Wayne and Lake Elsinore with 20 home runs, 81 RBIs and a .423 on-base percentage.