Educated at Windlesham House School, Malvern College and the Royal Military College, Sandhurst, Beauman was commissioned as a second lieutenant into the 2nd Battalion, South Staffordshire Regiment in 1908. Having served in South Africa before the First World War, Beauman's battalion was amongst the first units of the British Expeditionary Force (BEF) which went to France in August 1914: the "Old Contemptibles". After being invalided home in November 1914, he returned to the front in January 1915 when he served as Staff Captain, Deputy Assistant Adjutant and Quarter Master General, and then acting lieutenant colonel of the 1st Battalion of the South Staffordshires. In May 1918, he took command of the 69th Brigade on the Italian Front. He was made a Companion of the Distinguished Service Order (DSO) for an action during the Battle of Festubert on 16 May 1915, when he commanded the leading company of his battalion in an assault on enemy trenches; after reaching the line allotted to his battalion, his company held the position for three days under intense artillery fire. Beauman received a Bar to his DSO in November 1917, for an action in which he re-deployed his own battalion to support another on his right which was "in difficulties" during an enemy attack. The citation states that he "proved himself to be a leader of exceptional capability". He was also mentioned in despatches six times and was awarded two Italian medals.