The deal is worth $1.5 million and includes up to $750,000 in incentives.
The 39-year-old has belted 564 career home runs, five shy of 11th place on the all-time list. He batted .249 with 23 home runs and 74 RBIs in 107 games with the Chicago White Sox before being traded to the Los Angeles Dodgers on August 31.
"They were really excited about me coming there and so to me, it was a no-brainer," Thome told reporters.
"I've always enjoyed the way they've played and how they've gone about their business. To be a part of that, it will be a lot of fun to go there and help them win."
(Writing by Jahmal Corner in Los Angeles; Editing by John O'Brien)