In 1884–85 Baden-Powell became noted for his use of observation balloons in warfare in Bechuanaland (now Botswana) and the Sudan. From Oct. 12, 1899, to May 17, 1900, he defended Mafeking, holding off a much larger Boer force until the siege was lifted. After the war he recruited and trained the South African constabulary. On returning to England in 1903, he was appointed inspector general of cavalry, and the next year he established the Cavalry School, Netheravon, Wiltshire. He was promoted to lieutenant general in 1907.

Having learned that his military textbook Aids to Scouting (1899) was being used for training boys in woodcraft, Baden-Powell ran a trial camp on Brownsea Island, off Poole, Dorset, in 1907, and he wrote an outline for the proposed Boy Scout movement. Scout troops sprang up all over Britain, and for their use Baden-Powell's Scouting for Boys was issued in 1908. He retired from the army in 1910 to devote all his time to the Boy Scouts, and in the same year he and his sister Agnes (1858–1945) founded the Girl Guides (in the United States, Girl Scouts from 1912). His wife, Olave, Lady Baden-Powell (1889–1977), also did much to promote the Girl Guides. In 1916 he organized the Wolf Cubs in Great Britain (Cub Scouts in the United States) for boys under the age of 11. At the first international Boy Scout Jamboree (London, 1920), he was acclaimed chief scout of the world.

A baronet from 1922, Baden-Powell was created a baron in 1929. He spent his last years in Kenya for his health. His autobiography, Lessons of a Lifetime (1933), was followed by Baden-Powell (1942, 2nd ed. 1957), by Ernest Edwin Reynolds, and The Boy-Man: The Life of Lord Baden-Powell (1989), by Tim Jeal.