"Wully" Robertson was born at Welbourn, Lincolnshire. He began his military career in 1877 by enlisting as a private in the 16th Queen's Royal Lancers. At that time, the army was seen by many people as a refuge of last resort for paupers and 'ne'r do wells'. His mother was horrified. "I will name it to no one," he records her saying in his autobiography, "I would rather bury you than see you in a red coat."
He rose to Sergeant Major in 1885, his career being helped by a developing expertise in signalling and quartermasters' duties. Encouraged by his officers (and the clergyman of his old parish) he passed an examination for officer status and obtained a commission as a lieutenant in the 3rd Dragoon Guards. This was very unusual at the time. Those who had exceptional skills in supporting services were sometimes promoted to officer rank in the engineers or similar corps, but Robertson was commissioned as a cavalry officer. It would have been impossible for this to happen in Britain, as officers were expected to have a private income that would enable them to 'keep up appearances' and pay extravagant mess bills. In India, it was different. Active service officers with experience were needed, there was less accent upon social status and appearance, and the cost of living was very cheap.
He consequently served in India and completed a tour of duty with the Intelligence Corps. He was wounded and awarded the DSO in the Chitral relief expedition. Promoted to Captain, he attended Staff College at Camberley in 1896–97. Attendance at the Staff College indicated that he had been selected as an intelligent and promising officer, and graduates of the College were earmarked for 'fast track' promotion, capable of commanding military formations.
Robertson served as Intelligence officer to Frederick Roberts, 1st Earl Roberts, the British Commander-in-Chief South Africa, subsequently returning to the War Office to head up the foreign section of the intelligence department. He was subsequently commandant of the British Army Staff College.
Robertson served as Quartermaster General and then as Chief of Staff of the British Expeditionary Force (under John French) before being promoted to CIGS in December 1915. As CIGS, Robertson was a strong supporter of BEF commander Douglas Haig, and played a major role in the ousting of Prime Minister Herbert Henry Asquith and his replacement with a Tory-dominated coalition led by David Lloyd George. He was committed to a western front strategy focusing on Germany and against what he saw as peripheral operations on other fronts. This stance was at odds with Lloyd George's view that Britain's war effort ought to be focused on the other theatres until the arrival of sufficient US troops on the Western Front, and Robertson resigned as CIGS in February 1918. After the armistice, he commanded the British army of occupation in the Rhineland.
In 1919, Robertson was thanked by Parliament, granted £10,000 and created a Baronet, of Beaconsfield in the County of Buckingham. When he was promoted to field marshal a year later, he became the first man to rise in the British army from the lowest rank (private) to the highest (Field Marshal).
Robertson died in February, 1933, aged 73. He was succeeded in the Baronetcy by his son Brian Hubert. The latter rose to become a General in the Army and was raised to the peerage as Baron Robertson of Oakridge in 1961.