[4] In his debut match at the 2012 Olympics, he defeated Ghanaian boxer Duke Micah, having received a bye in the first round.

[8][9] Conlan won a silver medal at the 2013 European Championships in Minsk, losing to Welsh boxer Andrew Selby by 1:2.

[10] Conlan moved up from flyweight to bantamweight and on 2 August 2014 won the gold medal at the 2014 Commonwealth Games in Glasgow, beating England's Qais Ashfaq.

Conlan and his teammate, fellow Irish boxer Paddy Barnes, would compete in seven fights over 14 weeks in an effort to try and secure qualification for the 2016 Olympics in Rio de Janeiro.

[16] In the 2016 Olympic Games in Rio de Janeiro, Conlon endured "daylight robbery" by losing his quarter-final on a "truly awful verdict to a blood-spattered Russian" Vladimir Nikitin.

[22] On 23 September, Bob Arum confirmed that Conlan would be making his professional debut at The Theater at Madison Square Garden, on St. Patrick's Day.

[23] On 17 March 2017, Conlan won his first fight as a professional boxer, beating Tim Ibarra by a third round technical knockout (TKO) at the theatre at Madison Square Garden.

In front of a packed crowd in his hometown Belfast, Conlan continued his unbeaten streak in the pros and stopped his opponent in nine rounds.

[29] Conlan won his first bout at the super-bantam weight level on 30 April 2021, beating Ionut Baluta by a majority decision.

[37] In the men's bantamweight quarterfinal stage of the 2016 Summer Olympics in Rio de Janeiro, Conlan was eliminated by a controversial call, in which Russia's Vladimir Nikitin was awarded the victory.

[38] Conlan reacted by raising his middle finger at the judges and delivering a strongly-worded live television interview to RTÉ, accusing officials in amateur boxing of corruption.

[39][40][41] That decision was one of a number that had fellow international boxers and commentators questioning the integrity of Olympic boxing and the scoring system used.

[44] In his eleventh professional bout, Conlan arrived in Madison Square Garden with The Wolfe Tones' song Celtic Symphony playing and some of the crowd chanting "Ooh ahh, up the 'Ra".

[45] Some, including Northern Irish former world champion Dave McAuley, called for action from boxing regulatory bodies.