He competed in the 1904 Summer Olympics held in St. Louis, Missouri, in the all-round, which consisted of 100 y run, shot put, high jump, 880 y walk, hammer throw, pole vault, 120 y hurdles, 56 pounds weight throw, long jump and 1 mile run. He won the gold medal.
Kiely was thirty-four at this time. The British team had approached him with promises of his fare and expenses, and American sponsorship was also offered but, as a committed nationalist, he decided to go on his own, representing his native country. He raised the fare partly by selling many of the prizes he had won over the years and sailed for the States at the end of May.
In America he had several more offers to join the American or British teams. But again he declined and made it clear in statements carried in all the American papers of the time that he would represent only Ireland 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 hailed from Ballyneale just outside Carrick-on-Suir, County Tipperary, and achieved his gold in 1904 becoming the first Olympic multi-event track champion for 16 centuries. All ten events were held on the same day.