Born the son of Major Guy Melvil Gibbs and Margaret Gibbs (née St John) and educated at Eton College and the Royal Military College, Sandhurst, Gibbs was commissioned as a second lieutenant into the Kings Royal Rifle Corps (KRRC) on 31 December 1939, almost four months after the British entry into the Second World War. He was not immediately involved in action, however, as he was deemed to be too young, and remained in the United Kingdom until he was posted to the 2nd Battalion, KRRC, then commanded by Lieutenant Colonel George Erskine and in the process of reforming after sustaining severe casualties during the siege of Calais. Gibbs, promoted to lieutenant on 1 July 1941, was to serve with the battalion for the rest of the war and was deployed to North Africa with his battalion in late 1941, he was awarded the Military Cross (MC) on 15 October 1942. After participating in the Second Battle of El Alamein, he took command of 'C Company' of his battalion in March 1943 and remained in that role for the rest of the war. Commanding his company throughout the final stages of the Tunisian Campaign, taking part in the Allied invasion of Italy, the Normandy landings and the subsequent fighting in North West Europe until Victory in Europe Day (VE Day) in May 1945. Throughout this time, from D-Day to VE Day, one of his fellow officers was Edwin Bramall. Like Gibbs himself, Bramall was destined to reach the very highest ranks. He was awarded the Distinguished Service Order (DSO) on 2 August 1945.