Cousins, 27, was the Marlins' third-round Draft pick in 2006, and he has spent parts of three seasons in the big leagues.
Also on Wednesday, right-hander Sandy Rosario was claimed by the Red Sox.
The Marlins also outrighted infielders Donnie Murphy, Nick Green and Gil Velazquez to Triple-A New Orleans.
Cousins spent much of 2012 at New Orleans, where he batted .296 with seven home runs and 36 RBIs in 61 games. For the Marlins, Cousins appeared in 53 games and batted .163 in 86 at-bats.
Cousins plays all three outfield positions, and he arguably had the strongest throwing arm of any outfielder in the Marlins' organization.
Rosario, 27, opened the season as a closer at New Orleans. The right-hander was promoted to the big leagues on June 8, and he appeared in four games. But on June 16, he went on the disabled list with a right quad strain.
Murphy made Miami's Opening Day roster, and he appeared in 52 games, batting .216 in a utility role. Velazquez saw action late in the season at third base, and he finished with a .232 average in 19 games.
Green suffered a left thumb injury on Aug. 8 against the Dodgers, and was limited to seven games after he spent a majority of the season at Triple-A.
The five moves reshapes the Marlins' 40-man roster, which is now at 39 with four players on the 60-day disabled list.