Competing in the light welterweight division he faced Australian Luke Woods in the first round and was eliminated from the competition after a 0–10 loss.

[1][2] Following his defeat Donnelly was subsequently sent home from the Games by team management after drinking alcohol and causing a disturbance in the athlete's village.

[3] In his semifinal Donnelly was beaten on a split judge's decision by India’s Mandeep Jangra, meaning he finished with a bronze medal.

[5] He won five of his six fights, beating Kazakhstan's Madiyar Ashkeyev, Brian Ceballo of the United States, Puerto Rican Nicklaus Flaz Guillen, Alberto Palmetta of Argentina and Italy's Dario Morello, but was defeated by Venezuelan Gabriel Maestre and suffered a walkover defeat after visa issues meant he was unable to travel to fight Azerbaijan's Parviz Baghirov.

[5][6][7] Donnelly qualified to represent Ireland in the men's welterweight event at the 2016 Summer Olympics to be held in Rio de Janeiro, Brazil, via his fourth-place ranking in the World Series of Boxing.