[1] His grandfather was the prominent lawyer Sir James Mansfield, Solicitor General from 1780 to 1782 and in 1783 and Chief Justice of the Common Pleas from 1804 to 1814.

[5][6] In 1855, during the Crimean War, Mansfield was appointed military adviser to the Ambassador at Constantinople Lord Stratford de Redcliff, and accompanied him to the Crimea.

[1] He then returned to India and served as Chief-of-Staff during the Indian Mutiny campaign from 1857 to 1859, initially with the local rank of major-general.

His role during the Siege of Lucknow in November 1857 saw his appointment Knight Commander of the Order of the Bath (KCB) in March 1858.

[12] Sandhurst died in London on 23 June 1876, aged 57, and was buried at Digswell church, Hertfordshire.