Considered one of the founders of sociology of law in Norway and Scandinavia,[2] Mathiesen did extensive research on prisons, surveillance technology and the power structures within society.

[3] Besides criminologist Nils Christie, Mathiesen is one of two Norwegian social scientists covered in the book 50 Key Thinkers in Criminology (Routledge, 2009).

Mathiesen was known for his belief in the importance of combining academic work with social activism, maintaining focus on the legal context of prisons simultaneously with his sociological approach.

[13] He wrote in Norwegian and English, and several of his books have been translated into other languages, including Swedish, Danish, German, Italian, Portuguese, Spanish and Chinese.

Mathiesen's early concerns in the 1990s about the rise of data registration, and how this may arguably compromise personal privacy in society, were recognized as innovative views at the time.