Mariano began his political career working for Philadelphia city council member Daniel P. McElhatton. He ran against his former boss in 1995 and won, making him the representative for Philadelphia's seventhcouncil district. In 2005 he was arrested on charges that he exchanged political favors to pay off his credit cardbills. He was convicted and sentenced to six and a half years in prison, eventually being released in 2010 after serving just over four years of his sentence.