On Saturday, the 30-year-old right-hander was cleared to compete in Minor League games. He will start off at Class A Jupiter in the Florida State League on Monday.
Oviedo, formerly Leo Nunez, is winding down his eight-week suspension stemming from playing under a false identity.
The terms of the MLB-mandated punishment allowed him to begin pitching in Minor League games 16 days prior to the end of the suspension. The Dominican Republic native is eligible to join the Marlins on July 23.
"It's going to be like the biggest trade of the year," manager Ozzie Guillen said of Oviedo's return. "I will view that like a big trade that we make for the run. That kid is going to help the bullpen."
When he does, Oviedo will provide immediate help in the back end of the bullpen. No longer going by the name Nunez, Oviedo will commonly be called J.C.
He was the Marlins' closer from 2009-11, compiling 92 saves in 117 opportunities. He was 36-for-42 a year ago.
In his final year of being arbitration-eligible, he signed a one-year, $6 million deal in the offseason. But he's only being paid the prorated portion of his salary, which will be less than $3 million.
Having Oviedo gives depth at closer, as well. For instance, on Saturday, Heath Bell was not available because he pitched in four straight games. Oviedo would be the closer option on those days.
"That kid is going to be a big lift," Guillen said.