[1][2] Edgcumbe was returned to Parliament for Plymouth in 1859, a seat he held until 1861 when he entered the House of Lords on the death of his father.

[1][3] In 1879 he sworn of the Privy Council[4] and appointed Lord Chamberlain of the Household by the Earl of Beaconsfield,[5] a post he held until the government fell in 1880.

[10] Edgcumbe was also an Aide-de-Camp to Queen Victoria from 1887 to 1897 and a Member of the Council to the Prince of Wales from 1901 to 1917 as well as Keeper of the Seal of the Duchy of Cornwall from 1907 to 1917.

[1][19] On 9 February 1889, the Earl of Mount Edgcumbe was appointed Colonel in command of the Plymouth Brigade, consisting of the five Volunteer Battalions of the Devonshire Regiment and the two of the Duke of Cornwall's Light Infantry, which was charged with defending the Royal Navy's base at Plymouth in time of war.

They had four children:[1] After Lady Katherine's death in September 1874, Lord Mount Edgcumbe married secondly, his first cousin, Caroline Cecilia, daughter of George Edgcumbe and widow of Atholl Liddell, 3rd Earl of Ravensworth, on 21 April 1906.