Cuthbert remained in command of 13th Brigade when it was mobilised for service in the British Expeditionary Force after the First World War began in August 1914. He took the brigade to France and commanded it through the Retreat from Mons, the First Battle of the Marne and the First Battle of the Aisne. He was sent back to England at the end of September and placed on "invalid" status. He was succeeded by William Hickie. On 26 November, Cuthbert was appointed to take command of a Territorial unit; this was the 140th Infantry Brigade, which he had commanded in its peacetime incarnation as the 4th London Brigade, of the 47th (2nd London) Division. He remained with them through 1915 and 1916, culminating in the German attack on Vimy Ridge in May 1916, where Cuthbert led the division in lieu of the divisional commander, who was on leave. He was not a popular brigadier; the London volunteers particularly objected to his strict views on cleanliness, a story circulated that he had ordered front-line trenches to be swept out with brooms. He was nicknamed "Spit and Polish" by the infantry as a result of his obsession with appearances, alongside his earlier nickname of "Bluebell", which may have been a reference to a brand of polish.