Leaf Daniell of the Sword Club was captain of the British teams that visited Paris in 1906 and 1907. He was a member of the team again for the 1909 trip, which was under the captaincy of A. G. Ross. In between, Daniell was a member of the Great Britain team that won the épée silver medal at the 1908 London Olympics, the same year that he also won his only Amateur Épée Championship. He narrowly failed to retain it the following year when beaten by Robert Montgomerie after a tie.
The son of a London China and glass dealer, Daniell was a partner in the firm of art dealers A. & B. Daniell of Wigmore Street, London. His sister was the 1924 and 1928 Olympian Gladys Daniell who was four times the Amateur Ladies’ foil champion. She had won it in 1911 and 1912, but did not defend it in 1913 following Leaf’s death.