"It was an opportunity to add some pitching depth that we talked about," Marlins president of baseball operations Larry Beinfest said. "He's a left-handed pitcher with a great changeup. He has big league experience, which is important.
"We're very happy with Buck and Hayes. It's a good opportunity for John and a good opportunity for us to add pitching depth."
LeBlanc, 27, comes off a 5-6 season with a 4.63 ERA in 14 starts. He will compete for a back-of-the-rotation spot, knowing he has no guarantees. And if he doesn't make the Opening Day roster, the lefty has an option year left, so he can be sent to the Minor Leagues without the Marlins risking losing his services.
"There's a couple of spots they're looking to fill, and basically I'm in the mix for back-end jobs," LeBlanc said. "I'll go into Spring Training and try to do my thing and get ready for the season. If everything shakes out that way, I'll head to Miami at the end. If not, I'll continue to work and try to improve and make my way there at some point during the season."
The left-hander also made 17 starts at Triple-A Tucson, where he was 9-1 with a 4.30 ERA, logging 106 2/3 innings.
LeBlanc faced the Marlins in 2011, collecting a win in San Diego while giving up three runs in 5 1/3 innings. On Sept. 23, the lefty struck out 10 in seven innings while giving up two runs in a loss to the Dodgers.
"In the middle of the season, I made a couple of tweaks mechanically, to try to get a little better rhythm and a little more movement going towards the plate," he said of his success down the stretch.
The Marlins and Padres began talking about the LeBlanc-for-Baker deal last week at the General Managers Meetings in Milwaukee. Beinfest noted that the team is continuing to seek additional starting pitching.
Miami already is courting free-agent lefties Mark Buehrle and C.J. Wilson, who is expected to visit South Florida after Thanksgiving.
Baker, 30, missed most of last year as he recovered from Tommy John surgery to his right elbow. The left-handed-hitting catcher was called up in September, and he had 13 at-bats with two hits in 16 games.
He did appear in 15 Minor League games, batting .243 in 37 at-bats.
Baker, who broke in with the Marlins in 2008, is headed to his first year of arbitration.
A native of Alameda, Calif., Baker batted .299 with a .392 on-base percentage as a rookie in 2008. In 2009, he appeared in 112 games, hitting .271 with nine home runs and 50 RBIs.
In 2010, he was hindered by injuries, appearing in 23 games. He had Tommy John surgery on his right elbow later in the year and had some setbacks along the way this past year.
LeBlanc was a second-round pick of the Padres out of the University of Alabama in 2006. The left-hander has a 17-22 record with a 4.54 career ERA in 54 games (52 starts).
The Marlins started off 2011 with no left-handers in their rotation. Obtaining LeBlanc is the first of many offseason moves the Marlins are expected to make.
For LeBlanc, he will adjust to pitching professionally for a team other than the Padres.
"It's a bit bittersweet," he said. "San Diego is the only organization that I've ever known. But it's business. It's part of baseball. It's a fresh start. Hopefully, I can go to Jupiter and open some eyes and make the trip to Miami at the end of Spring Training."