Erskine was born in London, the son of Alan David Erskine Officer of the Most Excellent Order of the British Empire and Enid Rate. He was the grandson of Sir Henry David Erskine and the great-grandson of Francis Seymour, 5th Marquess of Hertford.
Erskine was educated at Winchester College and the Royal Military College, Sandhurst.
He commissioned into the Scots Guards on 1 May 1917, and in August 1917 he was deployed to the Western Front. Erskine was injured in October 1917 but returned to the front in October 1918. He served as Adjutant at the Guards Depot between 1921 and 1923, before serving as Regimental Adjutant of the Scots Guards until July 1932.
In September 1933 Erskine was promoted to major and between 1933 and 1935 undertook training at the Staff College, Camberley.
Between 1935 and 1939, he was Brigade Major, 1st Guards Brigade, and served with the brigade in the 1936-1939 Arab revolt in Palestine. Between 1939 and June 1940, Erskine was an instructor and then Commandant of the Tactical School Middle East, before becoming Commanding Officer, 2nd Battalion Scots Guards.
In 1942 he was Major-General Commanding Troops & Commandant Sudan Defence Force, and he was promoted to acting major-general in April that year. From 1943 to 1945 Erskine was Brigade Commander, 148 Pre-OCTU Training Establishments.
From 1945 and 1948 he was Provost Marshal of the Army at the War Office, and retired with the rank of major-general in May 1949.
