Lieutenant Colonel James Lynn, Royal Engineers, was born in 1804 in Suffolk. He was educated at Bury St Edmund's Grammar School and the Royal Military Academy at Woolwich, entering the Royal Engineers in 1826, and reaching the rank of 1st Lieutenant in 1831

In the 1st Carlist War of 1833-1840, a civil war in Spain, the British government supported the liberals, known from the names of the queen and regent as 'Isebelinos' or 'Cristinos', against the supporters of the claimant Don Carlos ('Carlists'), sending the British Auxiliary Legion, a volunteer force funded by the Spanish Crown, to Spain in 1835. The government also attached some regular military units to this force, including Royal Engineers. In 1837 Lieutenant Lynn was appointed as one of the Assistant Commissioners in the Headquarters of the Spanish (Isabelino) Army of the North, under the Commissioner Colonel Wylde, which was a joint military and diplomatic posting. In this capacity, he took an active part in the campaigns against the Carlists, and maintained correspondence with the Foreign Secretary, Lord Palmerston, and the ambassador in Madrid, George Villiers, later 4th Earl of Clarendon. There is a recital of his career in Spain in the certificate of service issued by the commander of the Army of the North, Don Baldomero Espartero, Duke of Victoria and Count of Luchana (see the original, with a translation, in MS. 11892/3, folder 5, items 10 and 11; and a later printed version, folder 6, item 2). From this we learn that Lynn took part in numerous actions between 1837 and 1840, and received a number of rewards and honours from the Spanish Government.

The statement of service held among the War Office records at the National Archives (WO 25/3913/1) notes that Lynn's period of 'special service' in Spain lasted until 16 Aug 1843. From July 1844 to June 1846 he was on special service in Prussia, and then from April to September 1847, on special service in Portugal (see MS. 11892/3, folders 3-4).

In 1843 Lynn was made 2nd Captain, and then Major. He was subsequently promoted to 1st Captain in 1847, and retired in 1850, being promoted to brevet Lieutenant Colonel in 1854. After his retirement he lived at Wickham Market, Suffolk, with his sister, Mary Emma Lynn, who was an amateur photographer (see the biographical appendix in Grace Seiberling and Carolyn Bloore, Amateurs, Photography, and the Mid-Victorian Imagination (University of Chicago Press, 1986). He died there on 12 November 1878 and was buried at Ufford.