Spencer Nilsen had a relatively short, yet memorable career in the gaming industry. Experiencing with his father's guitar and piano as a child, and performing in San Francisco Bay Area studios as early as age 14, it could be said that music came early into his life. Nilsen later went working in the concert industry, producing live shows for bands such as Aerosmith, The Police, and U2. This was followed by the creation of a production company, AdVenture Communications, with the lighting director and cinematographer Bill Holshevnikoff. They worked on various projects ranging from TV shows, commercials, and music videos.

In 1989, Nilsen released his first album on American Gramaphone Records, Architects Of Change. It featured a mixture of various genres, ranging from new age to classical, with some pop/rock and jazz influences. A few years later, he again released music through this record label, contributing one track for each of these albums by Chip Davis: Party Music That Cooks Vol.1 (1992) and Party Music That Cooks Vol.2 (1995). The tracks in question are titled "Good Question" and "Hydra's Laugh", respectively.

In 1992, Nilsen joined Sega of America by becoming the head of the music department and recording complex. The timing coincided with the release of the Sega CD system, thus he became part of most of Sega's CD projects up until the early Sega Saturn games. The CD format allowed him to create high-quality music with live instruments, himself playing the synthesizers/piano and other studio musicians (who became regular contributors) adding the guitars (Greg Strong, Erik Frykman), drums/percussions (Brad Kaiser), and more. David Young has been a frequent collaborator as a co-composer/producer/keyboardist. Nilsen also worked with the famous producer Gary Cirimelli on a few occasions, notably for the vocal remix of  "St. Gabriel's Mask" from Ecco: The Tides of Time. Unlike cartridges, the compact disc allowed the use of elaborated voices and Nilsen took advantage of this, featuring a rock theme song for The Amazing Spider-Man vs. The Kingpin by Mr. Big's vocalist Eric Martin and "Sonic Boom", the main theme of the USA version of Sonic CD performed by Pastiche, who also provided background vocals on many other tracks.

Since his departure from Sega sometimes in the end of the 90's, Nilsen has been busy writing music for TV and films. Two notable projects are Crashing Eden (1999) and No Return (2003). The latter earned him a Silver Medal at the Park City Film Music Festival. In more recent years, he has become part of the executive team at the Ex'pression College for Digital Arts in California. He occupies the role of President and Creative Director.

• Nilsen is also a producer, having worked with artists such as Rod Washington Moore and Bygone Dogs.
• In addition to composing music for Sega, he acted as a producer for other Sega soundtracks including Wild Woody. He also served as a musician, for example as the organist on "Who's Out There?" from the Mr. Bones soundtrack.
• There is a certain controversy around the Sonic CD soundtrack because it is different from the original Japanese/European version. In fact, Nilsen wrote completely new music for the USA release. A number of fans of the series consider this to be an outrage, prefering the original score by Naofumi Hataya, while others are more into the new one.
• He has been part of The Human Harmony Project (www.hhproject.org) along with Gary Cirimelli.