When the New Zealand All Golds toured in 1907, Hennessy joined the breakaway New South Wales Rugby Football League and was selected as the new code's first New South Wales captain. In October of that year Hennessy chaired a meeting of rugby identities with a view to creating a South Sydney rugby league club. The club was formed on 17 January 1908 and Hennessy was the inaugural captain-coach. For rugby league, Hennessy's place in the scheme of things is nothing less than extraordinary. When the new game of Northern Union (rugby league) arrived in Australia in the late winter of 1907, he enthusiastically stepped on board and when the New Zealand All Golds came to play the first of their historic three-game series against the locals at the Agricultural Ground (Sydney Showground) in August 1907, he was the NSW captain and coach. The games were played under rugby union rules as no one had a copy of the new code's laws. Hennessy subsequently read the rule book which arrived in Australia and declared: "This is a game for racehorses". Along with his fellow pioneers Hennessy was prepared to accept the ill-will that accompanied the splitting of the rugby code. "You had to take it on the chin and give it on the chin," he said. "Many good friendships tumbled to dust when we switched football codes." Hennessy stands as a monumental figure in the South Sydney story. It was at his home at 9 Chapman St, Surry Hills in October 1907 that the meeting was held which led to the formation of the Rabbitohs. Hennessy has sent a circular to all rugby union clubs in the district, convening the meeting. Because of that day and the events that followed, he can be fairly rated as the club's founder.