In December 1867, O'Neill became president of the Roberts faction of the Fenian Brotherhood, which in the following year held a great convention in Philadelphia attended by over 400 properly accredited delegates, while 6,000 Fenian soldiers, armed and in uniform, paraded the streets.
Fear of Fenian attack plagued the Lower Mainland of British Columbia during the 1880s, as the Fenian Brotherhood was actively organising in Washington and Oregon, but raids never actually materialised .