As a child, Mosaffa discovered his interest in story writing and English, contributing to his fluency in the language. He is a graduate of Civil Engineering from the University of Tehran where he showed an interest in acting; making his debut in the 1991 film, Omid. In the following year he won best male actor at the Fajr International Film Festival for his role in Darius Mehrjui's film, Pari. Mosaffa met his Future wife, Iranian Actress Leila Hatami on the set of Mehrjui's 1996 film, Leila. The two married in 1999 and have two children, a son named Mani (born February 2007) and a daughter named Assal (born October 2008).
Mosaffa's experience with directing began with the short films, Incubus, The Neighbour and the documentary feature, Farib-e-She'r or The Deceit of Poesy. He then directed his first film in 2005 with Sima-ye Zani Dar Doordast (a.k.a. Portrait of a Lady Far Away), starring Leila Hatami and Homayoun Ershadi. The film was shortlisted for the Sutherland Trophy, awarded to the Director of the most original first feature film screened at The Times BFI London Film Festival. His first feature film subsequently won the People's Choice Award at the Chicago International Film Festival and was nominated for the Crystal Globe at the 2005 Karlovy Vary International Film Festival. Mosaffa's second film, The Last Step /Pele ye Akhar, starring Leila Hatami has received acclaim from critics and audiences worldwide following its international premiere at the 2012 Karlovy Vary International Film Festival which gained Mosaffa the international critics' FIPRESCI prize for best film and awarded Leila Hatami with the Crystal Globe for Best Actress for her leading role in the film.
In October 2012, Mosaffa joined Oscar-winning Director of A Separation, Asghar Farhadi in Paris; starring alongside Bérénice Bejo and Tahar Rahim for Farhadi's first foreign language film, Le Passé or The Past which premiered at the Cannes Film Festival in May 2013.
