Schumaker is a .288 career hitter over eight seasons, all in St. Louis. He has played all three outfield positions, as well as second base.
The move seems to have been prompted by the recommendation of new Dodgers hitting coach Mark McGwire, who worked with Schumaker in St. Louis.
The Dodgers had been seeking a fourth outfielder, although their preference had been for a right-handed hitter.
Schumaker, 32, played a significant role in the Cardinals' World Series run in 2011, going 8 for 21 with four RBIs in the NLDS and World Series. He is a .305 career hitter against right-handed pitching.
The teams agreed to the trade on Tuesday night and Schumaker passed a physical on Wednesday to finalize the deal.
Lemmerman, 23, was a fifth-round pick out of Duke in 2010. He batted .233 with seven home runs and 46 RBIs with Double-A Chattanooga last season.
Schumaker was born in Torrance, Calif., and attended Aliso Niguel High in Orange County. He was a fifth-round pick of the Cardinals in the 2001 draft.
The Dodgers have had an active offseason, acquiring free-agent pitchers Zack Greinke, Brandon League and Ryu Hyun-jin at a combined cost of about $230 million, but Tuesday's trade is their first since a pair of blockbusters landed them Hanley Ramirez, Adrian Gonzalez, Josh Beckett and Carl Crawford last season.
Cardinals general manager John Mozeliak told the St. Louis Post-Dispatch last week that he was seeking to trade Schumaker, who will earn $1.5 million next season.
"We're trying to optimize the type of return we might get for him," Mozeliak told the newspaper.