However, he defended several of the United Irishmen in prominent high treason cases in the 1790s. Among them were the Revd. William Jackson, Archibald Hamilton Rowan, Wolfe Tone, Napper Tandy, The Sheares Brothers, Lord Edward Fitzgerald, William Orr and William Drennan. His difficulty in defending treason cases was that the Dublin administration could rely upon one witness to secure a conviction, while in England the law required that the prosecution had to use two or more witnesses. Consequently, his success depended on his lengthy examination of a single witness to try to find an inconsistency. He used this technique to great effect in the case of Patrick Finney, a Dublin tobacconist charged with treason in 1798, largely on the evidence of one James O'Brien. Curran destroyed O'Brien's credit and the judges, for once in sympathy with the accused, virtually ordered an acquittal. In the same year he unsuccessfully defended the journalist Peter Finnerty for seditious libel in publishing an attack on the judges who heard the William Orr case, and the Lord Lieutenant. Despite an eloquent speech by Curran, Finnerty was found guilty and sentenced to two years imprisonment.