By 1326 his influence was such that there were rumours of a conspiracy to make him King of Ireland; modern historians tend to dismiss the story, on the ground that the alleged conspirators were other magnates who were more interested in increasing their own power than aggrandising Desmond.

[3] Accepting the King's proposal, in addition to dealing with Munster and Leinster, he routed the O'Nolans and O'Murroughs, burned their lands in county Wicklow and forced them to give hostages.

He recovered the castle of Ley from the O'Dempsies, and had a liberate of £100 sterling dated at Drogheda 24 August 1335, in return for the expense he had incurred in bringing his men-at-arms, hobelars (light cavalry), and foot-soldiers, from various parts of Munster to Drogheda, and there, with Lord Justice Darcy, dispersed the King's enemies.

He was summoned by Writ dated at Westminster 10 July 1344, with Maurice FitzGerald, 4th Earl of Kildare, and others, to attend the King at Portsmouth "on the octaves of the nativity of the Virgin Mary", with twenty men-at-arms and fifty hobellars, at his own expense, to assist in the war against King Philip VI of France.

In 1345 he presided at an assembly of Anglo-Irish magnates at Callan, County Kilkenny, ignored a summons to attend the Irish Parliament and attacked Nenagh.

[6] By no means for the last time, the Crown evidently decided that it could not govern Ireland without the magnates' support: in 1348 Desmond was released, and in 1349 pardoned.