While studying medicine at Cambridge, Rocyn-Jones represented the University, but it was while at St Mary's Hospital, London, would gain his one and only cap for Wales, when he was selected to face Ireland as part of the 1925 Five Nations Championship.
The game took place at Ravenhill, Belfast, and Wales were led by Llanelli's Idris Jones.
Although Rocyn-Jones did not play for Wales again, he served the club later in his career, when, like his father before him, he was made President of the Welsh Rugby Union.
His presidency lasted a year, but his time coincided with the 1964-65 Triple Crown winning team.
Rocyn-Jones believed that the game was "essentially played for enjoyment and that too much emphasis could be placed on technical and tactical skill" .