Platt started his career at the Salford City Reds, making his début in Super League against the Wakefield Trinity Wildcats in the final game of the 2001 season at just 17. However he never quite made the grade and was released by the club.
Michael then signed for the Rochdale Hornets. His impressive début season was somewhat blighted by a broken jaw, although he did go on to win the National League's Young Player of the Year award in 2004.
Michael then joined the Castleford Tigers, and helped the Tigers gain promotion in 2005. Despite the subsequent Super League season proving to be difficult in a squad which lacked quality, Platt still managed to score 7 tries. However, after a heartbreaking 29–17 defeat against Wakefield in the final game of the season, Castleford were relegated.
Platt joined the Bradford Bulls in 2007 after a dispute between Platt and Castleford over his availability. His first season started well and he topped the try-scorers league for a number of weeks at the start of the season. He extended his contract in 2011 for a further 2 years, meaning he will stay with the Bulls until at least 2013.
In October 2014, Platt played in the European Cup competition.