His family was Catholic, a rather obscure cadet line of the Purcells, feudal Barons of Loughmoe in County Tipperary.

[1] As a young man Purcell served Ferdinand III, Holy Roman Emperor, in the Thirty Years' War against Sweden and France.

Purcell joined the Irish Rebellion of 1641 when it reached Munster early in 1642 and Richard Butler, 3rd Viscount Mountgarret with his rebel army entered County Tipperary from Leinster.

[11] In May and June 1642 General Garret Barry with the Irish Catholic Munster Army and Purcell attacked Limerick.

The town opened its gates willingly,[12] but the Protestants, led by George Courtenay, 1st Baronet, of Newcastle,[13] defended King John's Castle in the Siege of Limerick.

[20] In 1643, Muskerry led the Confederate Munster Army in an offensive against Murrough O'Brien, 6th Baron of Inchiquin in County Waterford.

[23] In the campaign of 1645, James Tuchet, 3rd Earl of Castlehaven commanded the Confederate Munster army in its fight against Inchiquin,[24] who had allied himself with the Parliamentarians.

[27] In 1646 the Munster army, under Edward Somerset, Earl of Glamorgan, who was favoured by Giovanni Battista Rinuccini, the papal nuncio, was sent to besiege Bunratty Castle near Limerick,[28] into which the Barnabas O'Brien, 6th Earl of Thomond, a Protestant, had admitted a Parliamentarian garrison in March.

[31] After a setback on 1 April, in which the garrison drove the besiegers from their camp at Sixmilebridge,[32] the Supreme Council replaced Glamorgan with Muskerry at the end of May.

[37] These fortifications abutted on the sea and Bunratty was supported by a small squadron of the Parliamentarian Navy under Vice-Admiral William Penn.

[53] On 12 June Muskerry, together with Lieutenant-General Purcell, rode over from the council meeting to the army's camp[54] where the troops acclaimed him as their leader and turned Glamorgan out of his command.

[58][59][60] Neither Glamorgan, not Muskerry, nor Taaffe stopped Inchiquin, who took Cappoquin, Dromana, and Dungarvan in May[61] and sacked Cashel in September.