[1] His brother, Mick O'Flanagan, was also a notable sportsman and also represented Ireland at both soccer and rugby union.
In the summer of 1937 he played for an Ireland junior team against a Birmingham FA XI at West Bromwich and scored twice in a 4–3 win.
His performance resulted in offers from Liverpool, Aston Villa and Manchester United, but his parents insisted that he complete his education.
In 1937 O'Flanagan began studying medicine at University College Dublin and it was while there that he developed into an all-round sportsman.
He continued to play soccer for Bohemian and on 7 November 1937, aged 18, he scored on his senior debut for Ireland against Norway, in a qualifier for the 1938 FIFA World Cup.
It was while at UCD that O'Flanagan first took up rugby union, playing for the university team, and in 1942 he received his first call up to the Ireland squad.
In 1941 he tied with David Guiney for the long jump title, but with only one gold medal available, he insisted his rival accept it as he already had one.
After qualifying as a doctor from UCD in 1945, O'Flanagan was offered a position as a junior GP in Ruislip, Middlesex.
He maintained his interest in sport, however, playing soccer for Arsenal and rugby union for London Irish.
When O'Flanagan began his international soccer career in 1937 there were, in effect, two Ireland teams, chosen by two rival associations.
He won 7 of these caps while playing for Bohemian and made his international debut against Norway on 7 November 1937, in a qualifier for the 1938 FIFA World Cup.
During subsequent decades he served on numerous bodies and held various positions in the areas of sports and medicine.