Niall Quinn played Gaelic football for the Robert Emmets club in Perrystown, Dublin 12. He also played underage football and hurling for Dublin. In July 1983, Quinn captained a Dublin Colleges GAA party on a one-month tour of Australia.
Aged 16, he played in the 1983 All-Ireland Minor Hurling Championship Final, and was offered a contract to play professional Australian rules football before settling on a career in soccer. He played Gaelic football for Co. Kildare club Eadestown after his retirement, winning a junior C county title in 2008.
"I learned my trade at Arsenal, became a footballer at Manchester City, but Sunderland got under my skin. I love Sunderland."
He played as a youth for Irish club Manortown United, which was based at Greentrees Park, adjacent to Robert Emmets GAC (it not being unusual in Dublin to play two separate codes of football). After an unsuccessful trial at Fulham he signed professional forms with English club Arsenal in 1983. He was signed as a centre-forward, but also had a brief spell as a centre-half for the Arsenal third team. After scoring 18 goals in 18 reserve matches in the first half of the 1985–86 season, Quinn was included in the first-team squad for a match against Liverpool. Quinn scored in the match as Arsenal recorded a 2–0 win. He made a further 11 league appearances for Arsenal that season, but failed to score as they finished seventh in the league. The end of the season brought Quinn his first call-up to the Republic of Ireland national team.
Quinn found himself playing under a new manager for the following season, as George Graham was appointed in place of Don Howe. Quinn had a regular place in the side that season, appearing in 35 league games and scoring eight goals. He also collected a Football League Cup winner's medal as Arsenal triumphed 2–1 over Liverpool. However, after Arsenal signed another target man, Alan Smith, in the 1987 close season, Quinn struggled to get into the team. Over the next three seasons he managed a total of just 20 league appearances and five goals – his three appearances in 1988–89 not being enough for a title medal. Quinn's lack of opportunities led him to submit a written transfer request at the start of the 1989–90 season. In total he scored 20 goals in 94 appearances for Arsenal, of which 81 were starts.