O'Sullivan began his club hurling career with Midleton. He enjoyed little success here and later transferred to Blackrock before moving to the St. Finbarr's club. In 1942 O'Sullivan played in his first countyfinal with "the Barr's". Ballincollig, a team who had defeated nine-in-a-row hopefuls Glen Rovers in the semi-final, provided the opposition. St. Finbarr's made no mistake and powered to a 5-7 to 2-2. It was O'Sullivan's first championship medal. Both St. Finbarr's and Ballincollig met in the championship decider again the following year. A 3-3 apiece draw was the result on that occasion, however, St. Finbarr's made no mistake in the replay and powered to a 7-9 to 1-1 victory. It was O'Sullivan's second championship medal.
Inter-county
O'Sullivan first came to prominence on the inter-county scene as a member of the Cork minor hurling team in 1938. He won a Munster medal that year following a remarkable 9-3 to no score victory over Kerry. The subsequent All-Ireland final was also a high-scoring affair. A 7-2 to 5-4 defeat of Dublin gave O'Sullivan an All-Ireland Minor Hurling Championship medal. In 1939 O'Sullivan announced himself at senior level when he scored a hat-trick of goals on his championship debut against Waterford. A further 4-3 to 3-4 defeat of Limerick gave Cork the provincial title and gave O'Sullivan his first Munster medal. The subsequent All-Ireland final pitted Cork against Kilkenny. In one of the most iconic championship deciders of all-time, played on the day that World War II broke out, the climax of which was played in a ferocious thunder storm. While a draw looked likely as the hour drew to a close Paddy Phelan sent a seventy-yard free in towards the Cork goalmouth. The sliotar was gobbled up by the defence and cleared, but only as far as Jimmy Kelly who sent it straight over the bar for a one-point lead. Immediately after the puck-out the referee blew the whistle and Cork were defeated on a score line of 2-7 to 3-3. Although defeated in the All-Ireland decider, Cork continued their breakthrough in 1940. An 8-9 to 6-4 defeat of Tipperary in the decider gave O'Sullivan his first National Hurling League medal. He added a second winners' medal to his collection in 1941 following a defeat of Dublin. An outbreak of foot and mouth disease severely hampered the 1941 championship. As a result of this Cork were nominated to represent the province in the All-Ireland series. O'Sullivan was a key member of the team in the final against Dublin, however, it turned into a one-sided affair thanks to contributing goals from Johnny Quirke and O'Sullivan himself. At the full-time whistle Cork had won by 5-11 to 0-6. It was one of the most one-sided championship deciders of all-time, however, it did give O'Sullivan an All-Ireland medal. O'Sullivan played no part on the Cork team the following year, however, he returned to the starting fifteen in 1943. A 2-13 to 3-8 defeat of Waterford that year gave O'Sullivan a second Munster medal. He later lined out in a third All-Ireland decider with Antrim becoming the first Ulster side to qualify for a final. Unfortunately, the occasion got to the Glensmen as Cork built up an unassailable 3-11 to 0-2 half-time lead. The final score of 5-16 to 0-4 gave Cork their second-ever hat-trick of All-Ireland titles while it also gave O'Sullivan a second All-Ireland medal. He retired from inter-county hurling following this victory.
Honours
Team
;St. Finbarr's
Cork Senior Club Hurling Championship : 1942, 1943
