Magan's historical notoriety originates from a single act. During April–May 1798 he informed the British government several times of the whereabouts of Lord Edward Fitzgerald on Thomas Street, just as the latter prepared to take the field at the head of thousands of Croppies during the 1798 Rising. Lord Edward's arrest on 19 May deprived the United Irishmen of their most charismatic leader, on whose head the British had put a price of £1,000, equivalent to £1.5m in 2015.