Hannon first came to prominence as a hurler with Ardscoil Rís in Limerick. Having played in every grade as a hurler, he was centre-back on the college's senior hurling team. On 11 March 2010, Hannon scored three points from play when Ardscoil Rís defeated Thurles CBS in the final of the Harty Cup. On 27 February 2011, Hannon was again at centre-back when Ardscoil Rís retained the Harty Cup title after a 3-19 to 0-03 defeat of C.B.S. Charleville in the final.
During his studies at Mary Immaculate College, Hannon was selected for the college's senior hurling team. On 27 February 2016, he won a Fitzgibbon Cup medal as Mary I won their first ever title after a 1-30 to 3-22 defeat of the University of Limerick after two periods of extra-time. Hannon, in spite of being substituted in the 79th minute and ending as the game's top scorer, said: "That was one of the most unbelievable games I have played in. We had it won and lost so many times throughout the game, but we’d have stayed until midnight to win."
Adare
Hannon joined the Adare club at a young age and played in all grades at juvenile and underage levels. He enjoyed championship success in the under-14 and under-16 grades before making his championship debut with the club's senior team as a sixteen-year-old. On 18 October 2009, Hannon scored three points from right wing-forward when Adare defeated Na Piarsaigh by 1-17 to 0-03 in the final of the Limerick Senior Championship.
Limerick
Minor and under-21
Hannon first played for Limerick at minor level. He made his first appearance on 25 June 2010 in a 1-17 to 2-12 defeat by Clare in the Munster Championship. Hannon subsequently joined the Limerick under-21 hurling team. On 3 August 2011, he scored 1-04 from play when Limerick defeated Cork by 4-20 to 1-27 in the final of the Munster Championship.
Senior
On 17 April 2010, Hannon made his senior debut at right wing-forward for Limerick in a National League defeat of Antrim at Loughguile. He later won a National League Division 2 medal after a 4-12 to 2-13 defeat of Clare in the final. On 14 July 2013, Hannon was at full-forward in Limerick's 0-24 to 0-15 defeat of Cork in the Munster final. Hannon's performances during the 2011 and 2014 seasons earned him All-Star nominations. In December 2017, Hannon was appointed captain of the Limerick senior hurling team for the 2018 season. On 19 August 2018, he scored two points from play and captained Limerick to their first All-Ireland title in 45 years after a 3-16 to 2-18 defeat of Galway in the final. Later that day Hannon was named on The Sunday GameTeam of the Year. He ended the season by winning an All-Star Award. On 31 March2019, Hannon was selected at centre-back for Limerick's National League final meeting with Waterford at Croke Park. He collected a winners' medal and the cup after contributing with a point in the 1-24 to 0-19 victory. On 30 June 2019, Hannon his first Munster Championship medal in six years after captaining Limerick to a 2-26 to 2-14 defeat of Tipperary in the final.
