Nightingall’s military and parliamentary careers were furthered by the Cornwallis family. No conclusive proof of his parentage has been found, but he may have been a descendant of the London merchants and salters William and Miles Nightingall who traded in Love Lane and Fore Street in the 1760s. He entered the army in 1787 and in 1788 was sent to Madras, becoming in 1790, following his service at the capture of Dindigul and siege of Palicatcherry, brigade major of the king’s troops in India. During the Mysore war he was appointed aide-de-camp to Colonel Nesbitt (1792) and the 1st Marquess Cornwallis (1793), serving with distinction at Pondicherry, Bangalore and Seringapatam. He returned to England with Cornwallis as brigade major of the eastern district, volunteered for the West Indies and was present at the capture of Trinidad in 1797. He became an extra aide-de-camp to Sir Ralph Abercromby† at Puerto Rico and inspector of the foreign corps before ill health brought him back to England in October; but he returned and was deputy adjutant-general in the capture of San Domingo in 1798. Sent home with dispatches, he undertook confidential missions for General Sir Thomas Maitland† in 1799 and served as assistant adjutant-general on the Helder expedition before joining Cornwallis in Ireland. He was Maitland’s deputy-lieutenant at Quiberon Bay in 1800. He married the East India Company chairman’s daughter that year ‘agreeable to her own inclinations but with my consent’ (Sir Lionel Darell), although their settlement had to be delayed pending decisions on his East Indian fortune; and after a period as quartermaster-general of the eastern district he attended the 1802 Amiens peace conference as Cornwallis’s military private secretary. Appointed quartermaster-general of the East Indies in 1803, he served at Agra and Leswarree before returning to Calcutta in 1805 as military private secretary to Cornwallis as governor-general. Sent to England in February 1807, he undertook a secret mission to Cadiz before serving as a brigade commander under Wellington at the battles of Rolica and Vimiero in 1808, for which he was mentioned in dispatches and received a medal and the thanks of Parliament. In December 1808 he was made commander-in-chief of New South Wales, but ill health prevented him taking up the appointment. After holding brigade commands at Hythe and Dover he returned to the Peninsula in 1810, and in 1811 commanded the first brigade at the battle of Fuentes d’Onoro, where he was wounded in the head. He was placed in command at Java in 1813 and knighted in January 1815. Despite opposition from the East India Company directors, he was posted to Bombay later that year.
His return for Cornwallis’s family seat at Eye at the 1820 general election came about unexpectedly following the corporation’s rejection of the sitting Member, the 2nd marquess’s brother-in-law, Mark Singleton.
Nightingall’s name was on a list of ‘more senior officers’ prepared when Sir George Murray* was considered as a possible commander-in-chief in June 1827, but he was no longer a serious contender for preferment.
