He was born about 1460, eldest son of Robert St Lawrence, 3rd Baron Howth and his first wife Alice White, daughter of Nicholas White, and heiress of the manor of Killester. His stepmother Joan Beaufort was a cousin of King Henry VII, to whom Nicholas, unlike most of the Anglo-Irish nobility, reminded steadfastly loyal. The date of his father's death and his own succession to the title is uncertain but it was probably before 1487.
The pretender Lambert Simnel appeared in Ireland in 1487, claiming to be Edward, Earl of Warwick, nephew of Edward IV, to whom he bore a striking resemblance, and thus to be the rightful King of England, his claim to the English Crown being far stronger than that of Henry VII, who had only a tenuous claim to the throne through his mother.. Simnel gained the support of most of the Anglo-Irish nobility, notably the powerful 8th Earl of Kildare, and was crowned as "King Edward VI" at Christ Church Cathedral in Dublin 1487. Nicholas, however, no doubt mindful of his own family's close connection to the Tudor dynasty, warned Henry VII of the impending invasion. Following Henry's triumph at the Battle of Stoke, Nicholas was rewarded with a substantial grant of money and the confirmation of his right to the Lordship of Howth. The King, however, could not resist playing a joke by inviting Howth and ten other Irish nobles, to a banquet at Greenwich in 1489 where, to their great embarrassment, they were waited on at table by Lambert Simnel, who had also been pardoned and made a kitchen boy.
Despite their differences over the Simnel rebellion, Howth became a close ally of Kildare, and he later challenged Thomas Butler, 7th Earl of Ormond to a duel on Kildare's account. He also quarrelled with Sir James Butler, Ormonde's cousin, who predicted, wrongly, that Nicholas' stout and bullish nature would end with his violent death. Kildare and Howth fought together at the notoriously bloody Battle of Knockdoe in 1504 between the forces of the Crown and the Burkes of Connaught. Howth is credited with urging the immediate attack which resulted in a victory for the Crown's forces.
Lord Howth was Lord Chancellor of Ireland from 1509 to 1513. O'Flanagan suggests that his entire training had been as a soldier, so that the appointment was presumably a tribute to his loyalty to the Crown, and his close links to Kildare, rather than due to his legal ability. On the other hand, his father had briefly held the same office, and his uncle Walter St. Lawrence and his brother Thomas St Lawrence were both distinguished lawyers, so it is likely enough that Nicholas also had some legal training. O'Flanagan also notes that his career as Lord Chancellor leaves no trace on the records, but that in the absence of any known complaints about his performance, he presumably fulfilled his duties adequately enough. The death of his great patron, the Earl of Kildare, in 1513 meant the end of Howth's political career; he was dismissed from the Lord Chancellorship and the Privy Council of Ireland and lived in retirement until his death in 1526.
Family
Lord Howth married three times and had children by each marriage. His first wife was Genet Plunkett, daughter of Christopher Plunket, 2nd Baron Killeen, by his wife Elizabeth Welles, daughter of Sir William Welles, Lord Chancellor of Ireland; his second wife was Anne, daughter of Thomas Berford, and widow of a Mr. Bermingham of Baldongan; and his third wife, who outlived him, was Alison Fitzsimon, daughter of Robert Fitzsimon, sister of Walter Fitzsimon, Archbishop of Dublin, and widow of Sir Nicholas Cheevers. After Lord Howth's death, Alison made a third marriage into the Plunkett family. He had eleven children, although it is not entirely clear which children were by which marriage. Christopher, the eldest son, must have been Jenet Plunkett's son, as his own wife was his stepmother Ann Berford's daughter by her first husband, while Alison was a child of the third marriage. The children were:
