He started his career as a roadie/light man for Hotshot, which was an early incarnation of the band Danger Danger and later was the band led by Mike Pont, the second Danger Danger vocalist.
He was replaced in Sweet Pain by Victor Prestin. He was badly injured in a motorcycle accident (at an intersection on the Sunset Strip in California) in October 1986, when he was still with Faster Pussycat. His leg was broken in seven different places, and he had to walk with a cane for a long time afterwards.
By the late-1980s, he had joined L.A. Guns. He remained with the group throughout their most commercially successful period. In addition to playing bass throughout his tenure with the group, he also sang lead vocals on the L.A. Guns song "Nothing Better To Do," from their 1995 album, Vicious Circle. However, he left the band shortly after this album was released. By the end of the 1990s, he was back in L.A. Guns, only to leave again in 2000.
He is married to Kelly Cunningham, the mother of actress Emma Roberts. Nickels also has a child with Cunningham, Grace Nickels, born in 2001. He is also the founder of the clothing line Montauk Salvage Company.