J. J. Walsh was born in the townland of Rathroon, near Bandon, County Cork. His family came from a farming background, "working a substantial holding of medium but well-cultivated land". Until the age of fifteen, Walsh attended a local school in Bandon, but by his own account "as far as learning went, I may as well have been at home". Together with his school-friend P. S. O'Hegarty, he passed the Civil Service exams for the Postal service. He later worked locally as a clerk in the Post Office. Like O'Hegarty, he spent three years in London at King's College, studying for the Secretary's Office "a syllabus (which) differed little from the Indian Civil Service". While O'Hegarty succeeded in his studies, Walsh did not, and returned to Cork where a friend, Sir Edward Fitzgerald, arranged work for him on the Entertainments Committee of the Cork International Exhibition.
Walsh was active in the Gaelic Athletic Association, promoting Gaelic games in many areas, but particularly in Cork city and county. His interest in organised sports had a strong political dimension.
I happened to be one of those who realised the potentialities of the G.A.A. as a training ground for Physical Force. Contamination with the alien and all his works was taboo. I gathered around me a force of youthful enthusiasts from the University, Civil Service and Business. With this intensely organised instrument, war was declared on foreign games which were made to feel the shock so heavily that one by one, Soccer and Rugby Clubs began to disappear.