O'Shea started playing darts at the age of 16. He won two All-Ireland darts titles with Cork and a European bronze medal playing for Ireland. O'Shea had his biggest career win at the
2019 World Masters, where he defeated
Scott Waites 6–4 in the final. He became the first Irish player to be crowned champion in the tournament's history. Originally ranked number 219 in the
British Darts Organisation rankings, he rose to number 59 and also earned qualification for the
2020 BDO World Darts Championship. At the BDO World Championship, he lost 3–2 to
Andreas Harrysson in the preliminary round. O'Shea earned a two-year
PDC Tour Card at
2022 Q-School after finishing ninth in the UK Q-School Order of Merit. He reached his first PDC ranking final in
Players Championship 14, losing 7–4 to
Michael Smith. He made his
PDC World Darts Championship debut at the
2023 World Championship, but lost 3–2 to
Darius Labanauskas in the first round. == Personal life ==