The Waterford man takes his pace in the 400 metres hurdles final at Rio 2016 – the last Irish person to compete in the final was Nenagh native Bob Tisdall, who won gold in the 1932 games in Los Angeles.
The race begins at 4 o'clock Irish time.
Elsewhere at the Olympics, Natalya Coyle Arthur Lanigan-O'Keeffe both begin their campaigns in the Modern Pentathlon.
Cork's Bryan Keane competes in the Men's Triathlon, which begins at 3pm.
Leona Maguire and Stephanie Meadow resume from 3-over par and 6-over par respectively ahead of the second round of the Golf tournament.
And the sailors Ryan Seaton and Matt McGovern compete in the Men's 49er Medal Race, which gets underway at five-past five.
