The Padres acquired left-handed reliever Trevor Seidenberger, a minor leaguer, from Milwaukee in the deal announced Thursday.
The 24-year-old Liriano played 38 games for the Padres in 2014, hitting .220 with one homer, six RBIs and four steals. He struck out 39 times in 109 at-bats.
San Diego had designated Liriano for assignment last week after signing free-agent shortstop Alexei Ramirez.
The Brewers designated outfielder Shane Peterson for assignment to make room for Liriano on the 40-man roster.