He attended the Sandhurst and was commissioned into the Royal Warwickshire Regiment as a lieutenant on 10 May 1882.
Kiggell left the Staff College in 1894, and for the next three years served as instructor at Sandhurst. Kigg, as he was commonly called, spent most of his duty thereafter in staff assignments. He saw action during the Boer War and in 1913/14 was commandant of the Staff College; he was promoted major general in 1914. His military ideas were exceedingly orthodox and plodding, but in an army where wealth and connection dominated, Kiggell had no choice as a man of only modest means but to work his way up in the staff in lieu of choice field commands.
Kigg served at the War Office during the first year of the Great War, and, in November 1915, was appointed assistant to the chief of the Imperial General Staff. The next month, however, his good friend Sir Douglas Haig, the new British commander in chief, brought Kiggell over to France as chief of the General Staff. It was a curious appointment since Kiggell had no experience in modern large-scale warfare since August 1914, having spent the early war years in England. Unfortunately, Kiggell and his staff proved to be not only generally mediocre but also highly subservient to Haig. It is perhaps ironic that in July 1916, in a fatal moment of independence, Kigg persuaded Haig to abandon small group attacks at the Somme in favor of assaults in successive waves, which were mercilessly cut down by enemy machine-gun fire.
Kiggell was serenely optimistic as late as August 1917 that the Germans could be displaced from the Belgian coast, and he pushed Haig to maintain the offensive during the Third Battle of Ypres to the point of canceling a planned tank offensive in the direction of Cambrai with General Julian Byng's Third Army for fear that this would divert forces and equipment from the vital Ypres sector. Despite flooded battlefields, heavy downpours, fields of mud, and the utter exhaustion of the British troops, Kiggell throughout October 1917 forced the drive on Passchendaele to continue. The slaughter of the campaigns of 1917 (400,000 British casualties alone at Ypres) resulted in pressure to remove Kiggell as chief of the General Staff in France; indeed, Kigg broke down owing to "nervous exhaustion" after visiting the Passchendaele front late in 1917 (after the fighting had ended). Early in 1918 he was sent to Guernsey as lieutenant governor and military head. Haig incredibly lamented his departure: "I am very loth to part with Kigg's help and sound advice." Kiggell was promoted lieutenant general in 1917; he died at Felixstowe on February 23, 1954. Generals Sir Henry Rawlinson and Sir Hubert Gough concurred that Kigg was well below standard as a staff chief.
Kiggell had married Eleanor Rose Field, daughter of a colonel, on 10 March 1888. They had three sons, born in 1890, 1894 and 1903. His wife died in 1948.