In 1899 came Mafeking, the most notable episode of his outstanding military career, by which he became a Major General at the age of only 43, and the hero of every boy. During the 217 day siege of Mafeking, Baden-Powell's book 'Aids to Scouting' was published and reached a far wider readership than the military one for which it was originally intended. Back in England in 1903, after organising the South African Constabulary, he found youth leaders and teachers all over the country using his book. He spoke at meetings and rallies and whilst at a Boys' Brigade gathering, he was asked by its Founder, Sir William Smith, to work out a scheme for giving a greater variety in the training of boys in good citizenship.

He published 'Scouting for Boys' in six fortnightly parts at 4d a copy. Sales of these books were tremendous. Soon boys, on their own initiative, began forming themselves into Scout Troops all over the country. Scouting spread quickly through the British Commonwealth and other countries. Baden-Powell, who was then Inspector General of Cavalry, retired from the Army in 1910 at the age of 53 to devote all his enthusiasm to the development of Scouting and its sister Movement, Guiding. In 1912, he married Olave Soames, who was his constant help and companion in all his work. Olave, Lady Baden-Powell, became known throughout the world as World Chief Guide.

At the first International Scout Jamboree at Olympia, London in 1920, Baden-Powell was unanimously acclaimed 'Chief Scout of the World' – a title which has never been held by another Chief Scout. He took the title Lord Baden-Powell of Gilwell – Gilwell Park in Chingford, London, being the Association's Leader Training Centre. Amongst the honours he received were degrees from six Universities, 28 foreign Orders and Decorations, and 19 foreign Scout Awards. In 1938, suffering from ill-health, he went to live in semi-retirement at Nyeri, Kenya. He died in 1941 at the age of 83 and is buried at Nyeri. On the headstone are the words 'Robert Baden-Powell, Chief Scout of the World', surmounted by the Scout and Guide Badges.