Sir Nicholas Malby (1530?–1584) was an English soldier active in Ireland, Lord President of Connaught from 1579 to 1581.
He was born probably about 1530. In 1556 his name appears in a list of persons willing to take part in the plantation of Leix in Ireland. On 6 August 1562 he was found guilty of coining, and, with three of his associates, was condemned to death; he was, however, reprieved on consenting to serve under Ambrose Dudley, 3rd Earl of Warwick, in France. A man of education, in April 1563 he is described as Warwick's secretary. In 1565 he was sent to Spain, where he was commended for his judicious conduct by Phayre, the English minister at Madrid. On his return to England he was sent to Ireland, and was shortly afterwards appointed sergeant-major of the army by Sir Henry Sidney. After the death of Shane O'Neill in 1567 he was stationed at Carrickfergus in order to assist Captain Piers in keeping the Scots of the Glynns in check. He was reproved by the lords justices for distraining Brian MacPhelim O'Neill's and other Irishmen's cattle for cess, but his conduct was justified by Sir Henry Sidney. His position was a difficult one, and he complained that he had to feed his men at his own cost, but he displayed tact in his management of Sorley Boy MacDonnell, and Sidney, on visiting the north in October 1568, found the charge committed to him in very good state. In July 1569 he was sent to the assistance of Sir Peter Carew against the Butlers, and in a skirmish near Carlow he was hurt by a fall from his horse. He was warmly commended by Sir William Fitzwilliam and Sir Edward Fitton, and on 22 March 1571 he obtained a grant of the office of collector of the customs of Strangford, Ardglass, and Dundrum.