Nicolson served in the First World War with the Harwich Force and took part in the Zeebrugge and Ostend Raids in 1918. After the war he joined the staff at the Royal Navy College, Dartmouth and then became Aide-de-camp to the Governor of Malaya and the Straits Settlements. He was appointed Captain of the aircraft carrier HMS "Pegasus" in 1935, Captain of the cruiser in 1936 and Captain of and Commander of the Tribal Destroyer Flotilla in 1938. Under Nicholson's command the "Somali" took possession of the Hannah Böge, the first prize of the Second World War at sea, just two hours into the war. He continued his war service as Commodore-in-Command, Royal Naval Barracks, Chatham from November 1940 to August 1943 and then appointed as Flag Officer, Ceylon from August 1943 to April 1944. He was then appointed Flag Officer, Ceylon and Deputy Commander-in-Chief of the Eastern Fleet until July 1945. After the war he became Admiral-Superintendent, Devonport until he retired in 1950.