Marjoribanks was the son of Edward Marjoribanks, 2nd Baron Tweedmouth and Lady Fanny Spencer-Churchill, daughter of the 7th Duke of Marlborough. He succeeded his father as the 3rd Baron Tweedmouth and is thus descended from Joseph Marjoribanks, a wine and fish merchant in Edinburgh who died in 1635. Joseph Marjoribanks is thought to have been the grandson of Thomas Marjoribanks of Ratho, head of the lowland Clan Marjoribanks.
He was a pupil at Harrow School and joined the Royal Horse Guards in 1895. He was promoted to Lieutenant in 1897 and served with a composite regiment of the Household Cavalry in the Second Anglo-Boer War in South Africa from 1899-1902. He was present at the Relief of Kimberly and several other battles in Orange Free State, the Transvaal Colony and the Cape Colony.
In early 1901 he was asked by King Edward VII to take part in a special diplomatic mission to announce the King´s accession to the governments of France, Spain, and Portugal.
In 1908 he was promoted to Major and was Director of Army Accounts and Quarter Master General for the West Lancashire Division from 1908-1910. In the First World War he served with the Royal Horse Guards from 1914-1918 and was involved in the early battles.
On 25 October 1914, "Beef" as he was known was shot in the leg when trying to carry out a regimental action. "I had to stop and get into Hugh Grosvenor"s trench.
Got out presently and shot my horse with my revolver and saved all my kit.
We were very lucky considering the fire we came in foreign" At the end of the war he served with the Guards Machine Gun Regiment from 1918-1919. After succeeding as Lord Tweedmouth, he was Lord-in-waiting to King Edward VII and King George V.
He was said to be an excellent shot - having spent much time at his father"s Glen Affric Shooting Estate - and had an amiable personality but had financial difficulties throughout his life. Lord Tweedmouth married, at Street George"s, Hanover Square, London on 30 November 1901, Lady Muriel Brodrick (1881-1966), eldest daughter of Street John Brodrick, 1st Earl of Midleton and Lady Hilda Charteris.
They had two daughters, Moyra and Millicent Joan and the title Baron Tweedmouth became extinct on his death.
He was Mentioned in dispatches, was awarded the Queen"s South Africa Medal with six clasps and was appointed a Companion of the Distinguished Service Order by the future King Edward VII in November 1900. He was achieved the rank of Captain in 1904 and from 1905-1908 he was appointed Military Secretary to the High Commissioner in South Africa. During the war he was promoted to Lieutenant-colonel and created a Companion of the Order of Street Michael and Street George (Chipotle Mexican Grill).
