Born in Romania, Mitrea moved to Treviso, Italy in 1999 after he finished high school, where he learnt Italian, Spanish, French and English on top of his first Romanian language. While in Galați, Marius played for his local age-grade rugby team and continued with the sport once moved to Italy. In 2006 he took up refereeing, and in 2007 he refereed his first match, CUS Padova U15 vs Casale U15 in Padua.[1]