Born on 7 September 1896 at Daylesford, Victoria, Stevens was the youngest child of Herbert Clarence Stevens and Violet Ophelia, née Bury. He attended schooling at Daylesford. He began working at the age of 12 at a cigar factory, before joining the Postmaster-General's Department as a clerk in the electrical engineers' branch in 1915.
First World War
Stevens enlisted on 2 July 1915 in the Australian Imperial Force in the Signal Corp and sailed for Egypt in November with the rank of corporal. He was promoted in March 1916 to sergeant and served with the 4th Divisional Signal Company. In June, he was sent to France and was awarded the Meritorious Service Medal for "devotion and keen sense of duty" during the battles of Pozières and the Ypres salient. He was transferred to the 5th Divisional Signal Company in February 1917 and was promoted to lieutenant in April. He saw action at Polygon Wood and was transferred to the Australian Corps Signal Company in March 1918. Upon arrival in Melbourne after the cessation of hostilities he was discharged from the Australian Imperial Force on 28 October 1919.
Between the wars
Upon returning home Stevens returned to work with the Postmaster-General's Department. He married Catherine McAllister Macdonald at the Presbyterian Church, South Melbourne on 26 April 1920. Rejoinining the Militia in 1921, he was promoted to captain in 1922 and commanded the 2nd Cavalry Divisional Signals and was promoted to major in 1924. He was promoted to lieutenant colonel in command of the 4th Divisional Signals, the 3rd Divisional Signals and the 57th/60th Battalion.
Following the outbreak of the Second World War, Stevens was seconded to the Second Australian Imperial Force on 13 October 1939 and placed in command of the 6th Divisional Signals. He was chosen in April 1940 as the commander of the 21st Brigade, and was promoted to colonel and temporary brigadier. Sailing with his brigade, he left for the Middle East in October. During the Syrian campaign against Vichy French forces in Syria and Lebanon he directed the battle of the Litani River on 12 June where he was wounded. For his actions during this battle he was awarded the Distinguished Service Order and was mentioned in despatches. After recovering from his wounds he led the brigades actions during the successful coastal advance towards Sidon and in the Battle of Damour between 5–9 July 1941. During the Syrian campaign against Vichy French forces in Syria and Lebanon he directed the battle of the Litani River on 12 June 1941 and, after recovering from wounds, he led the brigade's actions during the Battle of Damour between 5 and 9 July 1941. Stevens returned with the 21st Brigade to Australia in March 1942. Stevens was promoted to temporary major general and given command of the Militia's 4th Division in April before being appointed commander of Northern Territory Force in August. He was given the additional command responsibilities of the 12th Division and the Northern Territory Lines of Communications Area in December. Appointed the commanding officer of the 6th Division in April 1943 and oversaw the division's training on the Atherton Tableland, Queensland. Stevens deployed to the Territory of New Guinea in late 1944 for action in the Aitape–Wewak campaign, advancing along the coast to Wewak and clearing Japanese units from the Aitape-Wewak & Maprik area. The campaign inflicted heavy losses on the Japanese 18th Army. He was appointed the Companion of the Order of the Bath for "gallant and distinguished service" and "outstanding leadership in operations against the Japanese" in 1946. He was relinquished of command against his wishes in August 1945.