Loiseau thrived at Merrimack College finishing his career with 382 tackles, including 377 in his final three seasons, ranking him first all-time in school history. He broke the school record for tackles in a season with 133 in 2010 and was named All-American twice during his career. Loiseau was also twice named Northeast-10 Conference Defensive Player of the Year, marking the first time a Merrimack player earned that award on two occasions. Loiseau earned an invite to the 2012 NFL Scouting Combine, as well as playing in the East-West Shrine Game. In 2012 he signed with the Houston Texans attending training camp with the ball club. Loiseau then signed with the Indianapolis Colts in 2013 attending training camp with the AFC-South squad. Loiseau earned valuable Arena Football experience playing for the L.A. Kiss during the summer of 2014. Shawn was ultimately re-signed by the Colts spending the 2014-2015 season with the ball club. Loiseau has also played for the FXFL Hudson Valley Fort and most recently the Nebraska Danger of the IFL.