Harnedy had his first success as a student at
De La Salle College in
Waterford. He was part of the college's
Corn Uí Mhuirí-winning team in 1961. Harnedy also had club success at this time, winning three Duhallow divisional titles as a
dual player in 1960 and 1961. Harnedy later played both hurling and
Gaelic football with
University College Cork (UCC) during his engineering studies. He was part of the UCC senior teams in both codes that won the
SHC and
SFC titles in 1963. Harnedy added a second successive SFC title to his collection in 1964. His UCC career ended after winning the
Sigerson Cup title in 1966. Club and college successes resulted in Harnedy being selected for the
Cork under-21 football team. He won a
Munster U21FC medal in 1963 after a 2–03 to 1–04 defeat of
Kerry in the final. Harnedy first played for the
senior team in a
National League game in 1964. He made his sole
Munster SFC appearance in a 2–05 to 0–06 defeat by
Limerick in 1965. A move to
Carlow saw Harnedy join the
Éire Óg club and he won three successive
Carlow SFC titles from 1967 to 1969. He also lined out with
Carlow Town Hurling Club. ==Post-playing career==