The Marlins acquired from the Nationals first baseman Nick Johnson for lefty pitching prospect Aaron Thompson.
The deal, in the works heavily since Tuesday, was revived and consummated shortly before Friday's Deadline. Johnson is expected to join Florida on Saturday. To make room on the 40-man roster for him, Triple-A New Orleans infielder Andy Gonzalez was designated for assignment.
Johnson is making $5.5 million this season, and the Nationals are reportedly picking up $1.5 million of his remaining salary.
Thompson, 22, was one of five first-round picks of the Marlins in 2005, and in 20 starts for Double-A Jacksonville, the Texas native was 5-9 with a 4.11 ERA.
Typically, the Marlins don't like to part with pitching, and they usually seek pitching in return on any trades they make. But this trade was straight up, with Florida parting with a promising arm for the future for a veteran who is eligible for free agency after the season.
"We think highly of [Thompson], and they got a good player," Marlins president of baseball operations Larry Beinfest said. "We were willing to give to get. We think we have a good chance to qualify for the playoffs, and we wanted to help the team. Nick was the guy we wanted, and that was the price that it was going to cost."
Johnson, 30, provides a middle-of-the-lineup-caliber left-handed bat. In 98 games for the Nationals, he hit .295 with six home runs and 44 RBIs. Making him more attractive for Florida is his .408 on-base percentage.
Marlins manager Fredi Gonzalez said he plans on batting Johnson second, ahead of All-Star Hanley Ramirez, who leads the National League with a .343 batting average.
With men on base, Ramirez is especially dangerous. With runners on, he's hitting at a .396 clip.
"This guy is a quality guy. He's going to fit right in our clubhouse with our guys," Gonzalez said. "He knows the division. He's knows our guys. It's a good piece to have."
A slick fielder, Johnson will step in at first base, allowing Jorge Cantu to move across the diamond to third base.
Cantu is familiar with third, having played 129 games there in 2008. But this season, Cantu, who hits cleanup, has yet to make a start at third base. About once a week all season, he says, he took grounders at third base.
Emilio Bonifacio, who has been the regular third baseman, now will take on the role of a utility player, where he can play infield and outfield.
Bonifacio, a teammate of Johnson's last year in Washington, has been batting second the past few months. A speedster, he is hitting .248 with a .293 on-base percentage.
The Marlins acquired Bonifacio from the Nationals last November for Scott Olsen and Josh Willingham.
"One thing on Bonifacio, this isn't the end for him by any means," Beinfest said. "Hopefully, it's the beginning. I'm sure Fredi will spend some time with Boni. This is not an indictment on Boni. He's done a great job. He brings a lot of energy and speed to our team.
"This was an opportunity to change things up a little bit -- to hopefully make this team better, and Boni will be a big part of it."
Entering Friday, the Marlins were six games behind the Phillies in the NL East, and three games behind the Giants in the Wild Card standings.
Before finalizing its deal on Johnson, Florida explored several other opportunities. It was in the mix for San Diego reliever Heath Bell, but wasn't willing to part with either left-handed starter Sean West or Andrew Miller.
Reportedly, the Marlins entertained acquiring Blue Jays ace Roy Halladay, but the asking price included a prized prospect, outfielder Mike Stanton, who has been regarded as untouchable.
"We knew we wanted to add to this team," Beinfest said. "We believed in the guys. We poked around in a lot of areas. We looked at starting pitching. We looked at closers. We looked at bats. I think we looked at almost everything we could do to help the team. I think the starting pitching market, not surprisingly, was very rich as far as the asking price."
Now that the non-waiver Trade Deadline has passed, deals involving players on the 40-man roster cannot be made unless the players have already cleared waivers. In other words, the player must be offered to the other teams in reverse order of the standings, and if he is claimed by one of the teams, he cannot be traded. The club that placed the player on waivers can either withdraw the request and keep the player, or let the player go to the claiming team, which would then have the rights to the player.
Johnson broke in with the Yankees in 2001, and he's a career .273 batter with a .398 on-base percentage. Johnson played for New York during the 2003 World Series, won by the Marlins. The veteran has 20 games of playoff experience.
Marlins owner Jeffrey Loria has been a fan of Johnson for years.
"He's a special player, plain and simple," Loria said.
After the 2003 season, Johnson was dealt to Montreal as part of the Javier Vazquez deal. He played for the Expos in '04, and he's been with the organization since it moved to Washington in '05.
The 2003 Marlins received a boost in July when they obtained closer Ugueth Urbina from the Rangers. Adrian Gonzalez, now an All-Star with the Padres, was part of that trade.
Loria is hoping adding a veteran like Johnson will offer a similar boost to when Urbina was acquired six years ago.
"It's all about adding," Loria said. "This gives Hanley a little more protection.
"I liked our chances before, and I like them a little bit more now. Nick Johnson is a professional hitter -- a piece we needed. There is always that puzzle that seems to be pieces missing from time to time. I think he's going to be a big help."