Dias started his footballing career in 1981 for Salgaocar S.C. and stayed till 1989 when he moved to MRF FC. He stayed at MRF till 1993 and he signed with Churchill Brothers. He stayed at Churchill Brothers till he retired one year later in 1994.
On 13 July 2012 it was announced that Dias had been signed by the Churchill Brothers to become their new head coach. He was instrumental in Churchill brothers winning the I league for 2013 as head Coach. In 2014 Mariano Dias single-handedly coached Churchill brothers to their first Federation CupWin. Mariano was again in the limelight when he managed to assist Churchill Brothers Team to survive relegation from the I-League in the last 3 matches. He also revived the club in the Asian Football Confederation's Cup, Asian football second tier club competition.