During his animation career, Gruwell worked for Hannah-Barbera, Marvel, Film Roman, Disney, Filmation, Amblin, and Warner Brothers.
Gruwell was a member of the Motion Picture Industry Union.
The Los Angeles Times called Paul H. Gruwell "one of the last hand-drawn animation artists" in the movie industry.
Designed the short film "Basketball Jones" based on the song by Cheech & Chong in 1973. The cartoon notably appeared in 1979's Oscar-nominated film "Being There.".