Born in Ballyneale, just outside Carrick-on-Suir, Co Tipperary, Kiely competed in the 1904 Summer Olympics held in St. Louis, Missouri.

Kiely faced a monumental task in St. Louis; the ten events by which all-around ability was measured were all contested in a single day, in the following order: 100 yards, shot put, high jump, 120 yard hurdles, 880 yard walk, hammer throw, pole vault, 56 lb weight throw, long jump and one mile run.

When the English authorities learned that Kiely had been invited to the 1904 Olympics, they offered to pay his expenses on the condition that he represent the United Kingdom. As a committed nationalist, he decided to go on his own, representing his native country. Kiely travelled to America at his own expense and upon his arrival in New York, was offered further financial inducements by the New York AC, the Irish-American AC and the Chicago AC to represent them in St. Louis. Again, Kiely declined and it should be noted that apart from the Olympic nature of the St. Louis Games, they also served as the unofficial club championships of the USA; for this reason, the leading American clubs were anxious to have the Irish all-rounder on their team.

In America he had several more offers to join the American or British teams. But to their dismay, he declined and made it clear in statements carried in all the American papers of the time that he would represent Ireland and Ireland, only, in the Olympic Games. As Ireland was not independent in 1904 the IOC lists him as representative of the team of Great Britain and Ireland at the 1904 Summer Olympics.

Kiely achieved his gold in 1904 becoming the first multi-event track champion in the Modern Olympic Games. All ten events were held on the same day.