Hanahoe played both minor hurling and football with Dublin in the early 1960s. He played in the Leinster minor final of 1963, however, his side were defeated by Westmeath. Later that same year Hanahoe got trials with the senior team in both sports. He subsequently secured a spot on Dublin's senior football team and made his debut in 1964. In 1965 Hanahoe the left the Dublin team and put his sporting career on hold. He returned in 1970 when Kevin Heffernan was manager of the side. By this stage Dublin's football fortunes were at an all-time low. This low ebb culminated in a defeat by Kildare in the 1972 Leinster final. Hanahoe was captain that day and it was feared at the time that all the players would be sacked along with the management team.