He arrived at Drogheda in 1641, captain of a group of seventy-five which joined Sir Henry Tichborne's regiment the following year.
Cromwell aimed to suppress the alliance of the Catholic Confederacy and the previously defeated English Royalists.
Ponsonby was made governor of Dundalk in 1649 and impressed Cromwell with his strategy to capture Carrick in November that year.
Ponsonby was appointed as a commissioner to receive depositions from Protestants concerning "murders" committed by the Irish during the battles.
He also had a grant of lands in the same barony - Clanmaurice - that his younger brother Henry had benefited from, but his own claim was overriden by that of Colonel David Crosbie.
[1][2][7][5][6] Ponsonby renamed Kidalton Castle as Bessborough House in honour of his second wife Elizabeth ('Bess') (née Folliott), daughter of Anne Strode and Henry Folliott (the current house, now Kidalton College, was built seventy-seven years after his death).