Ross will give the Giants more depth for the final weeks of the playoff race. The Marlins will begin looking toward next year, and they plan to recall Cameron Maybin on Tuesday from Triple-A New Orleans for a late-season tryout in center field.
"Our playoff hopes have dimmed a bit, and we have to be realistic about that," Florida president of baseball operations Larry Beinfest said. "You can characterize it as whatever you want -- a white flag, or anything like that. We're realistic about where we are."
The move came shortly after the Marlins lost to Houston 2-1 to slip to 62-61.
Ross joined the Marlins in 2006 and became a favorite with fans and teammates. The decision by management left second baseman Dan Uggla red-eyed at his locker.
"Do I agree with it? No," Uggla said. "There's a long shot for us to get into this thing, and we're going to need him to do it, but they made their decision.
"Over the last five years, I've grown as close to Cody as I've grown to anybody, even in my own family. Everybody here in this organization and city is going to miss him."
Ross is batting .265 with 11 home runs and 58 RBIs. He has a salary this year of $4.45 million, which was the third-highest for the perennially cost-conscious Marlins, and he'll be eligible for arbitration this winter.
Ross said he had mixed emotions about the move.
"You play your heart out for this organization, and the next thing you know, you're gone," he said. "That's the game. That's the tough part. But there's a bigger plan for me, and I'm excited to get on that team. It is going to be a fun rest of the year for me."
Maybin hit .338 this year in Triple-A with four homers and 23 RBIs in 33 games. He has had several stints with the Marlins over the past three seasons, and this year he's hitting .225 for them with five homers and 19 RBIs in 51 games.
"The past couple of years he has struggled with the club and wasn't able to stick," Beinfest said. "We still think every highly of him. The talent and the tools are there. It is time for him to step up and do it."