1 May - Charles II repudiates his alliance with Irish Catholics in favour of one with Scottish Covenanters in the Treaty of Breda. Most English Royalists in Ireland surrender to the Parliamentarians after this point.
10 May - Battle of Macroom: Irish force defeated by English Parliamentarians.
17 May - Siege of Clonmel: Cromwell's troops storm the walls, taking up to 2,500 casualties. Although they are unable to take the town by force, the garrison, without supplies, slips away under cover of darkness.[2]
26 May - Cromwell leaves Ireland from Youghal and passes his command to Henry Ireton.