He played for four teams from 1998 to 2003, primarily the Oakland Athletics, where he was a teammate of his older brother Jason Giambi during the club's division championship-winning season in 2000.

Following his brother's departure to the Yankees as a free agent in the ensuing offseason, Jeremy saw declining playing time with three teams over the next two seasons before finishing his career in the minor leagues.

During Game 3 of the 2001 American League Division Series, Giambi was tagged out at home plate on the "flip play" by Derek Jeter.

[18][1] The following day, the Los Angeles County Medical Examiner announced that Giambi's death had been ruled a suicide via a gunshot wound to his chest.

[19] In June 2022, reports said that in August 2021, Giambi had been "struck in the head by a baseball and fractured his zygomatic bone" when serving as a pitching coach.