In June 1921, Sullivan turned professional and joined
rugby league side Wigan, reportedly signing a 12-year contract for a fee of £750. played , and scored 4-conversions in the 22-10 victory over
Warrington in the Championship Final during the
1925–26 season at
Knowsley Road,
St. Helens on Saturday 8 May 1926. played , and scored 2-conversions, and a
drop goal in Wigan's 15–3 victory over
Salford in the Championship Final during the
1933–34 season at
Wilderspool Stadium,
Warrington on Saturday 28 April 1934, and played in the 12–5 victory over
Dewsbury in the Championship Final second-leg during the
1943–44 season at
Crown Flatt,
Dewsbury on Saturday 20 May 1944 (
Joe Jones having played in the first-leg). Jim Sullivan played , and scored 4 conversions in Wigan's 20–2 victory over
Leigh in the
1922–23 Lancashire Cup Final at
the Willows in
Weaste,
Salford on Saturday 25 November 1922, played , and scored a conversion in the 11–15 defeat by
Swinton in the
1925–26 Lancashire Cup Final at The Cliff, Broughton on Wednesday 9 December 1925, played , and scored a conversion in the 2–5 defeat by Swinton in the
1927–28 Lancashire Cup Final at
Watersheddings,
Oldham on Saturday 19 November 1927, played , and scored a conversion in the 5–4 victory over Widnes in the
1928–29 Lancashire Cup Final the Willows, Salford, on Saturday 24 November 1928, played , and scored 2-conversions in the 12–21 defeat by Salford in the
1934–35 Lancashire Cup Final at
Station Road,
Swinton, on Saturday 20 October 1934, played , and scored 2-conversions in the 7–15 defeat by Salford in the
1935–36 Lancashire Cup Final at Wilderspool Stadium, Warrington on Saturday 19 October 1935, played , and scored a conversion in the 2–5 defeat by Salford in the
1936–37 Lancashire Cup Final at Wilderspool, Warrington on Saturday 17 October 1936, and played and scored 5-conversions in the 10–7 victory over Salford in the
1938–39 Lancashire Cup Final during the
1938–39 season at Station Road, Swinton on Saturday 22 October 1938. On 14 February 1925, he landed 22 goals against amateurs Flimby & Fothergill in the
Challenge Cup, which is still a record. He toured with the
Great Britain Lions three times (1924, 1928 and 1932) and was captain on the last occasion. He top-scored on all three tours. He refused what would have been a record fourth trip, in 1936, for personal reasons. For twenty years, he dominated at , representing Great Britain (28 times), Wales (26),
Other Nationalities (6), British Empire (1),
Glamorgan (1) and
Glamorgan and Monmouthshire (12). He was Wales' most capped player for over 70 years before his record was surpassed by
Ian Watson in 2010. During the
Second World War, he played infrequently for Wigan, as he chose to appear as a guest for a number of other clubs, including
Dewsbury,
Keighley and
Bradford Northern. His last season before retiring was in 1945–46 – the season when the peacetime league resumed – and played his last game against
Batley in February 1946. When he removed his Wigan jersey for the last time, he had made 774 appearances and amassed 2,317 goals and 4,883 points for the club. These figures are still unchallenged. He scored a club record of 161 goals in 1934-35 and a record total of 204 goals in 1933-34{{cite book ==Appearance record==