Mustelin was born in Åbo (Turku in Finnish), where he also spent his school years and studies. He matriculated in 1949 and studied physics at Åbo Akademi, graduating as a Ph.D. in 1963. He also studied Theoretical Physics for two years at MIT, Massachusetts Institute of Technology in Cambridge, MA, USA. He has worked at many places, including the University of Helsinki, Nordforsk, an institute for technological research cooperation among the Nordic countries: Finland, Sweden, Norway, Denmark, and Iceland; Tekes, Teknologian Edistämiskeskus ("Center for Advancement of Technology") and COST. After retiring he was a member of the board at the City of Helsinki, representing the Swedish People's Party.
Mustelin is known for his many scientific essays, articles and books, primarily his astronomic book Liv Bland Miljarder Stjärnor, Civilisationer i Vintergatan och Därbortom? ("Life Among Billions of Stars, Civilizations in the Milky Way and Beyond?"). The book, published in 1978, discussed how life had emerged and evolved on Earth, and how life could possibly exist on other planets and outside the solar system. It was translated from Swedish to Finnish, Norwegian, and Danish. He is also famous for inventing sporalogy, a humorous pseudoscience parodying astrology. He was the chairman of Skepsis ry (the Finnish association of skeptics) in 1989–1992.
Nils Mustelin was an expert in Classical Music with vast knowledge about composers, musicians and various facts, and could identify specific compositions by ear. For example, he memorized the entire catalog of Wolfgang Amadeus Mozart's work, and could name the assigned Köchel number given (e.g. K-13) to an individual composition. Nils Mustelin often appeared on TV and Radio in various panels and competitions, not only related to Classical Music, but also Sciences, such as Physics, Mathematics and Astronomy.
- Nils Mustelin obituary at www.kaupunginosat.net (in Finnish)
- Copy of Nils Mustelin web pages (mostly in Swedish and Finnish), created when Nils Mustelin was nominated as a candidate in the parliamentary election to be held in Finland in March 1999.