As an international, he captained Ireland and was a member of the team that won the 1914 British Home Championship. However, O'Connell is probably best remembered for managing several clubs in La Liga. In 1935 he led Real Betis to their first La Liga title and during the Spanish Civil War he took FC Barcelona on a tour of North America. Despite these successes, he died destitute in London in 1959.
O'Connell was born in 16 Mabel Street, Dublin on the eighth of March 1887, not far from the modern site of Croke Park. From age 14 he worked at Johnston, Mooney and O'Brien. He also played junior football with several local Dublin clubs, including Frankfort, Stranville Rovers and Liffey Wanderers, before joining Belfast Celtic. In March 1909, together with left-back Peter Warren, he was transferred from Celtic to Sheffield Wednesday for a combined fee of £50.
A terrific performer in the heart of the defence, O'Connell made his English First Division debut for Sheffield Wednesday against Bury on the last day of the 1908–09 season. However, in subsequent seasons he was unable to establish himself as a regular in the Wednesday first team due to competition from English McConnell, Jimmy Spoors and Bob McSkimming. As a result, he made just 21 senior appearances, 18 in the league and 3 in the FA Cup. However while with Wednesday, O'Connell made two of his six international appearances for Ireland.
O'Connell left Sheffield Wednesday for Hull City in March 1912 and subsequently made 58 Second Division appearances for City during the 1912–13 and 1913–14 seasons. While with City he also made a further three appearances for Ireland.
O'Connell's impressive performances with Ireland attracted the attention of Manchester United whom he signed for in May 1914 for a fee of £1,000. During the 1914–15 season he served as United team captain, made 34 First Division appearances and scored twice. He also played one further game for the club in the FA Cup. He made his league debut and scored his first goal for the club on 2 September 1914 in a 3–1 home defeat against Oldham Athletic. He scored his second goal on 10 April 1915 in a 2–2 home draw with Middlesbrough and made his final English League appearance for the club on 26 April in a 1–0 home win against Aston Villa.