Forsythe was released by the Brewers on Friday.
Forsythe signed a minor-league contract with the Brewers on Tuesday and was assigned to Triple-A Nashville, Will Sammon of The Athletic reports.
Forsythe was placed on the 45-day injured list Friday with a right oblique strain.
Forsythe is out of the lineup Sunday against the Mets, Jordan McPherson of the Miami Herald reports.
Forsythe is not in the lineup for the first game of Wednesday's doubleheader against the Orioles.
Forsythe signed a one-year, major-league deal with the Marlins and is batting sixth as the designated hitter Tuesday against the Orioles, Joe Frisaro of MLB.com reports.
Forsythe agreed to a contract Wednesday with the Marlins, Craig Mish of SportsGrid.com reports.
Forsythe was released by the Phillies on Saturday, Ken Rosenthal of The Athletic reports.
Forsythe will be part of the Phillies' 60-man roster.
Forsythe hit .348 with two doubles and three homers in 23 Grapefruit League at-bats this spring.