Francis Nathaniel Conyngham, 2nd Marquess Conyngham, KP, GCH, PC (11 June 1797 – 17 July 1876), styled Lord Francis Conyngham between 1816 and 1824 and Earl of Mount Charles between 1824 and 1832, was an Anglo-Irish soldier, courtier, politician and absentee landlord.
Conyngham was returned to Parliament for Westbury in 1818, a seat he held until 1820, and later represented Donegal (succeeding his deceased elder brother the Earl of Mount Charles) between 1825 and 1831. He served under the Earl of Liverpool as Under-Secretary of State for Foreign Affairs between 1823 and 1826 and under Liverpool, George Canning, Lord Goderich and the Duke of Wellington as a Lord of the Treasury between 1826 and 1830. In 1832 he succeeded his father in the marquessate and entered the House of Lords.
In July 1834 Lord Conyngham joined the Whig government of Lord Melbourne as Postmaster General, a post he retained until the government fell in December of the same year, and briefly held the same post under Melbourne again between April and May 1835. The latter month he was sworn of the Privy Council and appointed Lord Chamberlain of the Household. He remained in this position until 1839, when he was succeeded by his brother-in-law the Earl of Uxbridge.
Lord Conyngham was also Vice-Admiral of Ulster between 1849 and 1876 and Lord-Lieutenant of County Meath between 1869 and 1876. He was made a Knight Grand Cross of the Hanoverian Order in 1830 and a Knight of the Order of St Patrick in 1833.
On 21 September 1820, Conyngham purchased a cornetcy in the 22nd Light Dragoons, but this appointment did not take place, and he was replaced by his brother Lord Albert Conyngham, after he was appointed, without purchase, to be cornet and sub-lieutenant in the 2nd Regiment of Life Guards on 23 April 1821. He purchased a lieutenancy in the 9th Light Dragoons on 24 October 1821, and on 13 December, he exchanged from the half-pay of the 9th Light Dragoons into the 1st Regiment of Life Guards. He exchanged again, into the 17th Light Dragoons, on 3 April 1823, and purchased an unattached captaincy on 12 June 1823. Mount Charles, as he then was, entered the Ceylon Regiment, and purchased an unattached majority on 2 October 1827. He became a Major-General in 1858, a Lieutenant-General in 1866 and a full General in 1874.