Rendall was appointed as an Assistant Master at
Winchester College in 1887 and remained there for 37 years. In 1899, he was appointed as Second Master and then in 1911 as Headmaster, retiring at the end of the summer term of 1924. A devotee of Italian painting and sculpture, Rendall inspired his pupil
Kenneth Clark to appreciate the work of
Giotto,
Botticelli,
Bellini, and others. The
Winchester College War Cloister was a project of Rendall's to commemorate the 500 Wykehamists killed in the
First World War. In his early retirement, from 1924 to 1926, Rendall made tours of the
British Empire for the
Rhodes Trustees. In October 1926, Rendall was named as one of the five members of the newly constituted
Board of Governors of the BBC, with the
Earl of Clarendon,
Lord Gainford,
Sir Gordon Nairne, and
Mrs Philip Snowden. It was later reported that Clarendon was a Conservative, Gainford a Liberal, and Snowden a Labour supporter, while "Sir Gordon Nairne and Dr. Montague Rendall take no interest in any particular Party." In 1927, at the suggestion of Rendall, the BBC chose for itself the motto "Nation shall speak peace unto nation", inspired by a verse from the Book of Isaiah, "They shall beat their swords into ploughshares". Rendall was vice-chairman of the BBC from 1927 to 1933, when he retired. . Rendall was vice-president of the
Over-Seas League, the
Royal Empire Society, and
Framlingham College; Chairman of the League of Empire, the Public Schools Empire Tours Committee, and
North Foreland Lodge; a Member of the Education Committee of
East Suffolk County Council; and a Trustee of the Boyton Almshouses. ==Private life==