Oliver Leese was born to Second Baronet Sir William Hargreaves Leese in London, England, United Kingdom in 1894.

 

He was educated at Ludgrove School ,Wokingham, and Eton College 

 

Early in the First World War, he joined the British Army and was gazetted in the Special Reserve of Officers as a second lieutenant into the Coldstream Guards on 15 September 1914,[ later gazetted in the Land Forces on 15 May 1915. 

Despite receiving only five weeks of training, Leese was sent to France in mid-October 1914 and was posted to the 3rd Battalion, Coldstream Guards, part of the 4th (Guards) Brigade of the 2nd Division, near Ypres, Belgium. However, on 20 October, a week before Leese's 20th birthday, he was wounded, the first of three woundings he was to receive during the war, after being hit in the back by shrapnel.

He returned to England for treatment, and in 1915 returned to France, serving this time with the 2nd Battalion, Coldstream Guards, also part of the 4th Brigade, 2nd Division, where he experienced trench warfare throughout most of the year, in July suffered a second wounding, receiving multiple wounds to the face, but he remained on duty. In September his battalion, now transferred to the 1st Guards Brigade of the newly created Guards Division, fought in the Battle of Loos and, on 3 October, Leese was promoted to lieutenant. The next few months were spent holding the trenches, with no major engagements taking place

Leese was wounded for the third time during the Somme offensive in September 1916, an action in which he was mentioned in despatches and awarded the Distinguished Service Order

DSO citation (London Gazette November 1916)

"For conspicuous gallantry in action. He led the assault against a strongly held part of the enemy's line, which was stopping the whole attack. He personally accounted for many of the enemy and enabled the attack to proceed. He was wounded during the fight"

He was promoted to the rank of captain in 1921. Between 1927 and 1928, he attended the Staff College, Camberley, Surrey; he would strike a friendship with Bernard Montgomery while at Camberley. In Nov 1929, he was appointed as Brigade Major to 1st Infantry Brigade (Guards); a few days later he was formally promoted to the rank of major. In July 1933, he was promoted to the  rank of lieutenant-colonel. In Decembr 1936, he was promoted to the permanent rank of lieutenant-colonel. In Jan 1937, upon his father's passing, he was made the Third Baronet of the Leese Baronetcy. 

In September  1938, he was promoted to the rank of brevet colonel, followed by permanent colonel two months later after being posted to the Staff College, Quetta in India as an instructor. 

War in Europe broke out while he was in India. Returning in Britain in Mar 1940, he served as the Deputy Chief of Staff of the British Expeditionary Force in France. After being evacuated near Dunkerque, France on 31 May, he was given command of first 29th Infantry Brigade, then West Sussex County Division, and 15th (Scottish) Division in Jan 1941. In Nov 1940, he was promoted to the rank of  major-general, followed by a permanent promotion in December . In June 1941, he was made the commanding officer of the newly-formed Guards Armoured Division. In September 1942, he was assigned to the British Eighth Army in North Africa by the request of Montgomery to command the XXX Corps at the acting rank of lieutenant-general, and he would be with XXX Corps through the end of the Desert War and through the invasion of Sicily, Italy. In September  1943, he was promoted to the rank of brevet lieutenant-general. In December  1943, while in Britain, he was ordered to travel to Italy to take command of Eighth Army, where he would remain for about one year. 

In July 1944, he was promoted to the permanent rank of lieutenant general. In September , he was appointed the commanding officer of Eleventh Army Group; when he assumed command in November , it had been renamed Allied Land Forces, South-East Asia. 

Under his leadership, the Allies pushed through Burma, capturing the capital of Rangoon by May 1945, but conflicts between him and the field generals he inherited, namely William Slim, caused him grief. It culminated in 1945 when Leese's attempt to replace Slim with Philip Christison became his own undoing, resulting in Louis Mountbatten and Alan Brooke replacing Leese with Slim. 

Having lost his command in Southeast Asia, he returned to Britain to head up the Eastern Command, which was viewed as a demotion. 

His promotion to full general is believed to have been blocked by Mountbatten and Leese retired from the army in January 1947.

Leese became a noted horticulturist, writing books on cacti and keeping a well noted garden

In 1958, he served as the High Sheriff of Shropshire. 

Although a keen cricketer, he had only modest success as a batsman in the 1914 Eton XI and was relegated to 12th man for that year's Eton v Harrow match, but was President of the Marylebone Cricket Club in 1965

Oliver Leese died 22 January 1978 aged 83