Widengren wrote a series of works on Iranian religions (in particular Manicheism and Zoroastrism), Islam, Judaism, Gnosticism, etc.

Widengren studied history of religions at Stockholm University for his mentor Tor Andrae until 1933 and received his doctorate at the Faculty of Theology in Uppsala in 1936.

[2] Widengren was known for having mastered many languages, which gave him an advantage in the study of the frontiers of Asia during various eras.

Religious scholars in the 1960s critiqued these themes, but he continued to defend the importance of Iranian influence throughout his career.

[3] Widengren's position was continued and developed in many works by Alessandro Bausani and Shaul Shaked.