Thames passed a physical exam on Tuesday to make official a one-year contract that will pay him $1 million plus incentives.
Manager Don Mattingly has been pushing to add a right-handed power bat, and Thames has been the target since previous the front-runner, Bill Hall, signed with Houston.
Although his defense is considered shaky, Thames will be part of a three-way platoon with the left-handed-hitting Jay Gibbons and Tony Gwynn Jr. Thames can also play first base. Gwynn is best equipped to be the late-inning defensive specialist regardless of who starts.
A year ago, the Dodgers entered the season with Manny Ramirez as their starting left fielder, but Ramirez hit only eight home runs in 196 at-bats and was claimed off waivers by the White Sox. Gibbons hit five homers in 75 at-bats to resuscitate his career and was re-signed.
Thames' signing eliminates the need for an alternative outfield alignment focusing on defense that had been discussed, with Matt Kemp moving from center field to right, Andre Ethier moving from right field to left and Gwynn starting in center field.
"We think Marcus gives us a productive platoon we can pair with three left-handed-hitting candidates we've got -- Gibbons, Gwynn and [Xavier] Paul," said general manager Ned Colletti.
"At this point, moving Kemp and Ethier is a long shot. As of now, Kemp is the center fielder and Ethier is the right fielder. Gwynn has the ability to play all three positions, but that doesn't mean he'll take over for anybody."
Thames, 33, is coming off a 2010 season with the Yankees in which he hit 12 homers in 212 at-bats with a career-high .288 batting average. He hit a career-high 26 homers for Detroit in 2006 and is a career .248 hitter.
"Marcus helps balance us out a bit," Colletti said of the right-handed hitter. "We needed a right-handed bat, and this opens the door to add a left-handed hitter in the infield."
That could mean free-agent third baseman Eric Chavez, who is viewed as a possible part-time third baseman and left-handed bat off the bench. Chavez is coming off four years of back and shoulder injuries and is expected to work out for the Dodgers later this month.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.