Rob was born to a Jewish family in Calabasas, California and now lives in Los Angeles. He grew up in the same town as Incubus, and went to high school with some members of Hoobastank.

Rob started to play the drums at age ten after seeing an Aerosmith concert. His mother knew Joey Kramer, Aerosmith's drummer and was able to go backstage and see the entire production. Rob also plays the piano. When he was around thirteen, Bourdon played in bands with his friends. It was around that time he met Brad Delson, now the guitarist for Linkin Park, and they played together for about a year in a band called Relative Degree. Their goal was to play at the Roxy, and after achieving their goal with a sell-out show, they broke up.

He went to college at UCLA. Before joining the band he was a waiter.