Larkin simultaneously came to prominence with the James Stephens club at juvenile and underage levels, winning two county under-21 championship medals in 2000 and 2002.

After enjoying some success at underage levels, winning two under-21 championship medals, Larkin was a dual player with James Stephens in 2003.

James Stephens retained the county championship in 2005, with Larkin winning a second hurling medal following a 1–18 to 2–12 defeat of Ballyhale Shamrocks.

After a six-year gap, Larkin won a third hurling championship medal in 2011 after a thrilling draw, followed by a 1–20 to 0–15 replay defeat of Ballyhale Shamrocks.

[17] Kilkenny's bid for a third successive All-Ireland title ended in dramatic fashion as a late point from Kerril Wade handed Galway a narrow 1–15 to 1–14 victory.

Kilkenny were back in form that year, with Larkin winning a first National Hurling League medal following a huge 3–20 to 0–15 victory over Clare.

On 3 September 2006 Kilkenny faced a Cork team who were presented with the opportunity to become the first side in nearly thirty years to secure three successive All-Ireland championships.

[24] On 2 September 2007 Kilkenny faced defeated Munster finalists and surprise All-Ireland semi-final winners Limerick in the championship decider.

Kilkenny got off to a flying start with Eddie Brennan and Henry Shefflin scoring two goals within the first ten minutes to set the tone.

In a disappointingly one-sided final, Kilkenny produced a near perfect seventy minutes as Waterford endured a nightmare afternoon.

A 23-point winning margin, 3–24 from play, only two wides in the entire match and eight scorers in all with Eddie Brennan and Henry Shefflin leading the way in a 3–30 to 1–13 victory.

[30] On 6 September Kilkenny were poised to become the second team ever in the history of hurling to win four successive All-Ireland championships when they faced Tipperary in the decider.

For long periods Tipp looked the likely winners, however, late goals from Henry Shefflin and substitute Martin Comerford finally killed off their efforts to secure a 2–22 to 0–23 victory.

"The Cats" lost talisman Henry Shefflin due to injury, while Tipperary's Lar Corbett ran riot and scored a hat-trick of goals as Larkin's side fell to a 4–17 to 1–18 defeat.

2012 began well for Larkin, who by now was captain of the team, when he collected a fourth National League medal following a 3–21 to 0–16 demolition of old rivals Cork.

Galway stunned the reigning champions with two first-half goals, however, Kilkenny's championship debutant Walter Walsh gave a man of the match performance, claiming a 1–3 haul.

The 3–22 to 3–11 Kilkenny victory gave Larkin a sixth All-Ireland medal, while he also had the honour of lifting the Liam MacCarthy Cup.

[41] Kilkenny's dominance showed no sign of abating in 2013, with Larkin winning a fifth National League medal following a 2–17 to 0–20 defeat of Tipperary in the decider.

[42] In 2014 Larkin collected his sixth league medal, as Kilkenny secured a narrow one-point 2–25 to 1–27 extra-time victory over Tipperary.

After a two-year hiatus and a period of uncertainty surrounding the competition, the Railway Cup returned in 2012 with Leinster facing Connacht in the decider.

Larkin joined the Wicklow county hurling team as a coach under the managemeant of Éamonn Scallan ahead of the 2021 season.