Nilsson entered 32 Formula One Grand Prix races, qualifying for all of them. He won the 1977 Belgian Grand Prix at Zolder while driving for Team Lotus. After losing his Lotus seat, he signed for Arrows for 1978, but was later diagnosed with testicular cancer which meant he could not drive the car. However, he did compete in three International Race of Champions (IROC) races in 1977. He had two sixth-place finishes and a fifth-place finish.