Iajour began his career at his hometown club Raja Casablanca, in 2003. After staying there for four years, he moved to FC Chiasso.
FC Chiasso
In August 2007 when the Arabian Clubs Tournament was finished, Mouhcine decided to stay in Switzerland without the permission of his club Raja Casablanca. On 28 October 2007, Iajour has appeared for the first time in official match with the team of FC Chiasso.
Return to Raja Casablanca
He returned to Raja Casablanca in 2012. After a season, he won his first league title with Raja. In 2013, Raja qualified to FIFA Club World Cup as league champions of host country. On 11 December 2013, Iajour scored a goal in the 2–1 victory against Auckland City FC, in the play-off for quarter finals. His team eventually defeated Monterrey with 2–1 in the quarter finals to pass in the semi-finals. On 18 December 2013, he scored a goal in the historical 3–1 victory against Atletico Mineiro in the semi-finals. But in the final, Raja Casablanca was defeated by UEFA Champions League holders, Bayern Munich with 2–0. Iajour become one of the FIFA Club World Cup top scorers for 2013, together with Dario Conca, César Delgado and Ronaldinho. He received the FIFA Club World Cup bronze ball.[3]
In January 2020, Iajour returned to Morocco to play for RS Berkane.[6]
MA Tétouan
On 4 September 2023, Iajour returned to play in his former club MA Tétouan.[7]
International career
Youth
In the 2005 FIFA World Youth Championship Iajour has scored three goals and helped Morocco to move to the semi-finals, where they were defeated 3–0 by Nigeria. Morocco ended the tournament in fourth place after a 2–1 loss to Brazil.