In 1908, Hennessy was Souths' first hooker and, with Billy Cann, one of the club's first two delegates to the New South Wales Rugby Football League. He coached Souths in their 1908 NSWRFL season's final. In that foundation season he also had the honour of captaining Australia in its first ever rugby league Test – against New Zealand. Hennessy played in both Tests in May against New Zealand as captain, both of which Australia lost. Hennessy was selected to play in the first ever trans-Tasman test, which was the debut match of the Australia national rugby league team. He is listed in the Australian Players Register as Kangaroo No. 1. In July of that inaugural season he made another representative appearance captaining New South Wales in a 43-0 whitewash of Queensland in the first ever Australian interstate match.