His first school band was The Phaetons, which mutated into The Grim Reapers (which later included Tom Petersson in its line up). The Grim Reapers became Fuse which released one poorly received studio album before disbanding in 1970. Nielsen joined Nazz for a short time (replacing Todd Rundgren) before forming the short-lived Sick Man of Europe in Philadelphia in 1972 with Tom Petersson, and drummer Bun E. Carlos joining soon after. In 1973, Nielsen, together with Carlos, formed Cheap Trick. Petersson joined later that year, and Robin Zander joined in the fall of 1974. Nielsen wrote almost all of the songs for Cheap Trick's first few albums.