Diarmuid O'Sullivan (born 27 July 1978) is an Irish hurling coach and hurler who plays for Cork Premier Championship club Cloyne.

A fan favourite who was noted for his swashbuckling style during his inter-county career, O'Sullivan is considered a "Cork legend".

At inter-county level, O'Sullivan was part of the successful Cork under-21 team that won back-to-back All-Ireland Championships in 1997 and 1998.

From his debut, O'Sullivan was ever-present as a defender and made a combined total of 110 National League and Championship appearances in a career that ended with his last game in 2008.

As a dual player at the highest level, he won a Munster Championship medal with the Cork senior football team in 2002.

O'Sullivan announced his retirement from inter-county hurling on 12 May 2009, instead opting to transition to rugby, where he had stints with Cork clubs Highfield[4] and Midleton.

At inter-provincial level, O'Sullivan was selected to play in five championship campaigns with Munster, with his sole Railway Cup medal being won in 2000.

His father, Jerry O'Sullivan, played with the Cloyne club from the 1960s until the 1990s before later serving as an administrator with the Cork County Board and the Munster Council.

On 20 October 1996, O'Sullivan was at left wing-back when Cloyne drew with Newtownshandrum in the final of the Cork Intermediate Championship.

On 31 October 2004, O'Sullivan was at right wing-back when Cloyne qualified to face Na Piarsaigh in the final of the Cork Senior Championship.

[11] Cloyne qualified for a second successive Cork Senior Championship final with Newtownshandrum providing the opposition on 16 October 2005.

He was a regular in the half-back line throughout the 1996 championship and was at left wing-back when Imokilly drew with Avondhu in the final on 22 September 1996.

O'Sullivan subsequently progressed onto the Cork under-21 team and won a Munster Championship medal at full-back on 30 July 1997 following a 1-11 to 0-13 defeat of Tipperary.

O'Sullivan won a Munster Championship medal on 21 July after being introduced as a substitute in Cork's 1-23 to 0-07 defeat of Tipperary in the final replay.

[26] O'Sullivan ended the season by being nominated for an All-Star, but lost out to Kilkenny's Noel Hickey for the full-back berth.

O'Sullivan won his fourth Munster Championship medal on 26 June 2005 after a 1-21 to 1-16 defeat of Tipperary in the final at Páirc Uí Chaoimh.

O'Sullivan was in his usual position of full-back, and proved effective in nullifying the threat of Niall Healy who was substituted in the 56th minute.

[33] Cork subsequently qualified for a fourth successive All-Ireland final, with Kilkenny providing the opposition for the third time.

O'Sullivan received an early yellow card for an off-the-ball incident with Martin Comerford, while in the 29th minute he failed to deal with a high ball which bounced out of his hand towards Aidan Fogarty and a goal was conceded.

[37] The three players were later restored to the starting fifteen, however, Cork's championship campaign ended with an All-Ireland quarter-final replay defeat by Waterford.

[41] O'Sullivan missed Cork's National League campaign in 2009 due to the players withdrawing their services for the third time in seven years.

[46] His first season as part of the management team saw Cork lose all five of their group stage games in the National League before narrowly avoiding relegation with a 2-22 to 0-25 defeat of Galway in a play-off.

[48] O'Sullivan's second season as a selector saw Cork reach the National League quarter-finals where they faced a 1-20 to 1-18 defeat by Limerick.

[49] On 9 July 2017, he was part of the management team that saw Cork win the Munster Championship after a 1-25 to 1-20 defeat of Clare in the final.