Cousins fills the roster spot vacated by Chris Coghlan, who was optioned to Triple-A on Wednesday night.
Manager Ozzie Guillen says he plans on giving Cousins a look in center field. But on Friday, with the Rays going with left-hander Matt Moore, right-handed hitting Justin Ruggiano started for Miami.
"I am going to take a look at this kid, Cousins, to see what he can do," Guillen said. "In the meanwhile, we need to win games."
With Emilio Bonifacio expected to be out until about the All-Star break, the Marlins have been looking for a center field option to step up.
Coghlan was given an opportunity, but he was hitting .140 average at the time he was optioned. Bryan Petersen and Kevin Mattison also had chances.
Cousins can play all three outfield positions. He has one of the strongest arms for an outfielder in the organization.
At New Orleans, he added seven homers and 32 RBIs in 50 games.
"I feel really good," Cousins said. "I've been hitting the ball well all year. I'm coming in on a hot streak, lately. I'm just worrying about what Ozzie told me in camp, which was to keep it simple, and not care so much.
"Just go out and let the ability take over. I go out there and am aggressive. Steal bases when I can, and try to make every play I can make in the outfield and hit the ball hard."
Cousins has appeared in 75 big league games, including 48 in 2011. Last June 14, he went on the disabled list with a lower back strain.
Cousins was in the mix for a backup outfield spot in Spring Training, but he was optioned to Triple-A New Orleans on March 23.
In 89 career MLB at-bats, Cousins has a .202 average with one home run and six RBIs.
Until Bonifacio returns, Guillen is hoping somebody sticks in center, because he doesn't like making so many roster moves.
"For me, the most embarrassing things for me is when you send guys down every other week," the manager said. "But, in the meanwhile, those guys have to look at themselves in the mirror. Why am I getting sent down? I hope I can find one and stick with one. It would be easier for us."