Seymour studied Art in Melbourne, and taught himself how to play the bass guitar. In his spare time, he played in local bands and worked on the set of films like The Leonski Incident. At the end of 1984 he became the bass player for what was to become Crowded House. He stayed with the band until its demise in 1996. Nick also produced all artwork for the band, including costumes and stage sets.
He has worked on different projects since 1996, like playing in the band Deadstar and producing the debut album for Irish band Bell X 1. He has also moved to Ireland.
He is the brother of Mark Seymour, the lead singer in the now-defunct Australian supergroup Hunters and Collectors.