O'Riordan has spent his whole career so far at Munster Senior League side College Corinthians in the Republic of Ireland, playing for the club's youth teams over the last few years.

During his time in the Republic of Ireland, the 19-year-old was part of an Under 17s side who lifted the 2021/2022 FAI U17s Centenary Cup, as well as the Under 18s team who were crowned 2022/23 Cork Youth Leagues U18s Premier League Champions. He also helped College Corinthians reach the final of the FAI Youth Cup during the 2022/23 season, starting the match as they faced St. Joseph's.

He now makes the switch to Welsh football, joining Gresford Athletic to be an exciting, attacking option in the wide positions.

Gresford Athletic First Team Manager Eddie Maurice-Jones says that O'Riordan will fit into the way the that the team plays:

"Rian has impressed during training these last few weeks.

"He is a skilful and direct winger, who will suit our style of play, and he will add valuable competition and a different option in our attack."