Having served in the navy from 1812 to 1816, he studied law and was called to the bar at the Inner Temple in 1825. His work as a barrister, however, was confined principally to peerage cases before the House of Lords, and his time was mainly devoted to genealogical and historical studies. In 1831 he was made a knight of the order of the Guelphs, and in 1832 chancellor and knight-commander of the order of St Michael and St George, being advanced to the grade of the grand cross in 1840. He became a member of the council of the Society of Antiquaries in 1826, but soon began to criticize the management of the society's affairs, and withdrew in 1828.
He then criticized the Record Commission, which he regarded as too expensive. These attacks, which brought him into controversy with Sir Francis Palgrave, led in 1836 to the appointment of a select committee to inquire into the public records. He was also responsible for several reforms at the British Museum. In 1822 Nicolas married Sarah (d. 1867), daughter of John Davison of Loughton, Essex, a reputed descendant of the Tudor statesman William Davison. By her he left two sons and six daughters. Pecuniary difficulties compelled him to leave England, and he died near Boulogne on the 3rd of August 1848. Although a sharp and eager controversialist Nicolas was a genial and generous man, with a great knowledge of genealogical questions.
The most important of the works of Nicolas is his History of the Orders of Knighthood of the British Empire; of the Order of the Guelphs; and of Medals, Clasps, &c., for Naval and Military Services (London, I 841-1842). Among his numerous other writings are:
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