John Óge Kirwan served as Mayor of Galway for the term 1530-1531, followed by Thomas (1534–1535) and Richard (1550–1551), along with numerous bailiffs, sheriffs, and aldermen.
Many were forced to emigrate to the West Indies as indentured servants and in this way the basis of new wealth was accrued in the succeeding generation.
During Kirwan's lifetime, Ireland, led by the ports of Galway and Cork, was the principal external supply route for provisions to the islands; the annual value of beef exports in 1685 alone was 45,000 pounds.
While he supported the Jacobite side during the Williamite War in Ireland, he surrendered on terms to General Ginkel, was pardoned, and was allowed to hold his property.
The last member of the family to bear the name, Sir Denis Kirwan Bernard, died unmarried in 1956 and was buried on the summit of Cnoc Meadha.