After leaving school aged 15, Collins took the British Civil Service examination in Cork in February 1906. In 1910, he moved to London where he became a messenger at a London firm of stock brokers, Horne and Company. While in London he lived with his elder sister, and studied at King's College London. He joined the London GAA and, through this, the Irish Republican Brotherhood, a secret, oath-bound society dedicated to achieving Irish independence. In 1915, he moved to the Guaranty Trust Company of New York where he remained until his return to Ireland the following year.