Hamels went 14-9 last season with a 2.79 ERA in 32 games last season.
The one-year deal allows Hamels and the club the luxury of discussing a long-term contract. Hamels is eligible for free agency following the 2012 season.
The left-hander made $9.5 million last season in the final year of a three-year contract.
The club also signed Wilson Valdez for $930,000.
Tuesday was the final day for players to sign before arbitration numbers are exchanged.