Forbes joined the Royal Navy in July 1894. After serving as a Midshipman in the Channel Fleet and Pacific, he returned to the UK to train as a gunnery specialist. During the early part of World War I he served in HMS Queen Elizabeth. His service in her included the Dardanelles and Gallipoli campaigns. In October 1915 Forbes returned to the UK to take up an appointment as Flag Commander to Admiral Jellicoe, Commander-in-Chief of the Grand Fleet. He saw action at the Battle of Jutland from Jellicoe's flagship HMS Iron Duke.
After the end of the war Forbes had successive shore appointments, serving as Naval Member of the Ordnance Committee from October 1919 to March 1921 and then as Deputy Director of the Staff College, Greenwich, from August 1921 to June 1923. A sea appointment followed as Forbes returned to his old ship HMS Queen Elizabeth as her Captain.
Four years later came the high point of Forbes career when he became Commander-in-Chief, Home Fleet, an appointment he held from April 1938 to December 1940.
Charles Forbes died on 28 August 1960.