He last pitched as Leo Nunez. His 2011 season ended abruptly in September after officials discovered he had been playing under a fake name since he turned professional in 2000.
Oviedo was issued a new visa last week after clearing up his immigration status in the Dominican Republic, and now that he's back in the United States, he can begin serving an eight-week suspension from Major League Baseball for age and identity fraud.
He'll be eligible to rejoin the Marlins on July 23 and expects to be ready.
"With my name Juan Carlos Oviedo, I'm the same guy," he said in Spanish through a translator. "It's the same arm."
Oviedo will begin a minor league rehabilitation assignment two weeks before he's eligible to join the Marlins.
"It's good to have closure. Now it's time for him to get ready to hopefully help us later this summer," president of baseball operations Larry Beinfest said. "His name has changed. I'm hoping the stuff is the same, and we think it is. That's an awful big arm with a lot of experience to add at the end of July."
Oviedo saved 92 games for the Marlins in 2009-11, including 36 last year, and the Marlins gave him a $6 million, one-year contract this offseason. But with his availability uncertain, they also signed All-Star closer Heath Bell, and Oviedo will have a setup role when he returns.
During spring training, manager Ozzie Guillen joked that Nunez would pitch the seventh inning and Oviedo the eighth.
Oviedo said he'll be happy with any role.
"If they put me in in the seventh or the first inning, it doesn't matter," he said. "All I want to do is play."
Oviedo has said he began using a fake name as a youth so he could say he was old enough to sign a pro contract. When the fraud was finally discovered, he feared his career might be finished.
"I was scared," he said. "There are no words to explain how happy I am now that I have my name. My dad's name, who died, which is what he wanted for me."
Major League Baseball, the players' association and several lawyers were involved in clearing up the situation. Oviedo's status was still in doubt when the Marlins began the season in their new ballpark amid considerable hoopla.
"I had the Marlins channel in my house. I was watching them," Oviedo said. "Many times I would turn the channel off because I would feel a little sad.
"I feel very happy that I am here. That's all that I wanted to do -- be in the United States to return to my team and help."