The 36-year-old Grilli has enjoyed a career renaissance in Pittsburgh since originally signing with the Pirates in July 2011. He went 1-6 with a 2.91 ERA in 64 games in 2012 and struck out 13.8 batters per nine innings, fourth-best in the National League.
The signing also gives the Pirates some flexibility in the bullpen next year in case it ever decides to part ways with closer Joel Hanrahan.
Grilli has spent the majority of his career as a middle reliever but has struggled staying healthy until arriving in Pittsburgh. He has been a mainstay in the seventh and eighth innings with the Pirates because of his ability to get strikeouts in key situations.