Mostafaei states that he appealed forty death sentences of juvenile defendants during his work in Iran, of which eighteen were overturned. Four of his clients were executed in 2008 and 2009.[2]
Mostafaei became widely known for his work on human rights cases specially on death penalty and stoning cases in Iran and defense of Sakineh Mohammadi Ashtiani, a woman condemned to death by stoning for adultery. He wrote a series of blog posts on her case, attracting international attention and protest.[4] The stoning sentence was commuted in July 2010 in the face of world pressure.
During the case, Mostafaei's wife, father-in-law, and brother-in-law were imprisoned in what Radio Free Europe/Radio Liberty described as "an apparent attempt to pressure him to back down."[5] Mostafaei then illegally crossed the border into Turkey and sought asylum in Norway. The Norwegian government granted the asylum, Foreign Minister Jonas Gahr Støre calling Mostafaei "a courageous man who raises cases -- difficult cases -- which the authorities don't like".[2] A Mostafaei stated that though the case had forced him to leave Iran, he felt he had made the right choice: "I had a nice house, a good job, nice office, a good car. Iran was my home but it was not important."[6] He continued to work on human rights issues in Norway, describing himself as "maybe 10 times more [active]" than he had been in Iran.[6]
In 2011, Norwegian PEN awarded Mostafaei its Ossietzky Award, an "annual prize for outstanding achievements in the field of free expression".[7]
In 2012 Mohammad Mostafaei, established Universal Tolerance Organization (UTO) in Norway.[8]