[3] In the 2008 European Union Amateur Boxing Championships in Cetniewo, Poland, competed at Heavyweight earning victories over Stephen Simmons from Scotland (15:6) in the quarter-finals and Germany's Vahagn Sahakyan (10:7) in the semis.

In the final he faced the favoured Greek boxer Helias Pavlidis, against whom he lost on points (12:29) earning a silver medal.

[5] In his last national elite championships, Sheehan earned a points victories over Jason Barrons, Niall Kennedy and clubmate Dean Gardiner to clinch the 2014 Irish Super Heavyweight title.

[citation needed] In 2015, Sheehan moved to the USA to train under Virgil Hunter at King's Boxing Gym in Oakland, California.

Sheehan made his professional debut on 19 January 2016 against Jonathan Rice in Club Nokia, Los Angeles, California, United States.