Bayliss was the son of William Bayliss and Gertrude, the sister of physiologist E.H. Starling. Leonard Bayliss studied at the University College School before going to Trinity College, Cambridge in 1922. He continued for his PhD as a Michael Foster Student and his thesis was on "tone in plain muscle." He was a Sharpey Scholar from 1926 to 1929 and from 1928 he visited University of Pennsylvania on a Rockefeller Fellowship, working on micropuncture techniques to study the kidneys of frogs under A.N. Richards.[1]
Bayliss then went to work at the Marine Biological Laboratory at Plymouth before becoming a lecturer at the University of Edinburgh. During World War II, he worked for the Army Operational Research Group, studying the accuracy of anti-aircraft guns. In 1946 Baylisshelped establish the graduate course in physiology at University College.[2]
Bayliss married M. Grace Eggleton, who had studied under E.H. Starling, his uncle. Bayliss died on 20 August 1964.