A nine-year veteran who has played for Texas, Houston and Minnesota, Lamb hit .233 with one homer and 32 RBIs in 81 games with the Twins this year.
He was released Thursday after being designated for assignment, and will not be eligible for Milwaukee's postseason roster if the Brewers advance to the playoffs for the first time since 1982.
The 33-year-old gives the slumping Brewers another option for third along with Bill Hall, Craig Counsell, Joe Dillon, Mat Gamel and Vinny Rottino. Russell Branyan went on the 15-day disabled list on Aug. 14 because of an oblique strain.
The left-handed hitting Lamb is batting .257 against righties this year .067 (2-for-30) against lefties, while Hall is hitting .317 against lefties and .172 average against righties.