Reidy was an outstanding schools player with St.Patrick's College of Castleisland, and won the 2003 Dunloe Shield. He won two Munster Minor Football Championship medals with Kerry, and was a member of the Kerry minor side beaten by Laois in the 2003 All-Ireland Minor Football Championship semi-final and of the team which lost to Tyrone in the 2004 final. He lined out with the Kerry Under 21's between 2005 and 2007. He enjoyed little success however, losing to Cork in 2005 and 2006, as well as a surprise loss to Clare in 2007.
The Scartaglin man made his National Football League debut in 2006, against Mayo. He first broke through not the Kerry team in 2007 playing in that seasons National Football League. He made his championship debut against Waterford in the Munster Senior Football Championship on June 3. He played in the corner-back spot vacated by Tom O'Suullivan, who moved to full-back following the retirement of Mike McCarthy. Despite his inexperience and early difficulties, Reidy settled well and is recognised as a talented young back who blossomed during the Championship. He won his first Munster Senior Football Championship title after over coming Cork in the final. He gave fine performances against Mark Vaughan of Dublin GAA and James Masters of Cork in the All-Ireland Senior Football Championship semi-final and final. Reidy played at corner-back as Kerry won the final by 3–13 to 1–09 against Cork GAA. The victory made him the first Scartaglin player to win a senior All-Ireland with Kerry. He played in all of Kerry's National Football League games in 2008, including the final loss to Derry Reidy also had a fine year with his club, which won the East Kerry Intermediate championship. As a result, the club qualified for the East Kerry Senior Football Championship proper, surprisingly reaching the semi-finals and almost beating the powerful Dr. Crokes in what was described as a "David and Goliath battle". At divisional level however, Reidy's St. Kieran's sides were knocked out in the second round of the Kerry Senior Football Championship by eventual champions Feale Rangers. In 2008, Reidy has so far retained his number four jersey and is one of the starting corner-backs for Kerry in the National Football League.
