The Rockies also declined their side of a mutual option on the contract for Aaron Cook, making the 32-year-old right-hander a free agent.
Giambi, 40, hit .260 with six doubles, 13 home runs and 32 RBIs in 131 at-bats for Colorado last season.
In his three seasons with the Rockies, Giambi has hit .254 with 21 home runs and 78 RBIs, including three walk-off home runs and three pinch-hit home runs. Over his 17-year career, the California native has batted .281 with 428 home runs, 1,397 RBIs and 1,314 walks in 2,103 games.
He ranks 39th on Major League Baseball's all-time walks list, 42nd on the home run list and 71st in RBIs.
Cook has been with the Rockies his entire career, but is coming off a tough season in which he went 3-10 with a 6.03 ERA after opening the year on the 60-day disabled list with a broken finger.
The 6-foot-3 veteran had an $11 million mutual option for 2012 after completing a three-year, $30 million deal last season. He is now free to negotiate with any club, including the Rockies.
Cook is Colorado's all-time leader in wins (72), innings pitched (1,312 1/3) and starts (206) in a 10-year Major League career in which he's posted a 72-68 record with a 4.53 ERA. He was an All-Star in 2008, going 16-9 with a 3.96 ERA.
The Rockies now have 32 active players on their 40-man roster, in addition to five players on the 60-day disabled list.