Near Carrick they were joined by John O'Mahony, a landed proprietor of the neighbourhood, afterwards to become famous as the founder of Fenianism.

By descent, education and character a leader of men, O'Mahony had thousands of followers among the people ready to rally to any venture for Ireland at his call.

"His square, broad frame," wrote Meagher, "his frank, gay, fearless look; the warm forcible headlong earnestness of his manner; the quickness and elasticity of his movements; the rapid glances of his clear full eye; the proud bearing of his head; everything about him struck us with a brilliant and exciting effect, as he threw himself from his saddle and, tossing the bridle on his arm, hastened to meet and welcome us.

At a glance we recognised in him a true leader for the generous, passionate, intrepid peasantry of the South." O'Mahony strongly advised them to begin the insurrection that night in Carrick, and he left to collect the peasantry.

O'Brien and his comrades proceeded to the town where the people received them with frenzied enthusiasm, calling out to be led immediately to the fray.