L.E.W. Bevan qualified as a Member of the Royal College of Veterinary Surgeons (MRCVS) in London in 1904. Later that year both he and C.E. Gray* attended a brief post-graduate course in pathology and bacteriology at the Royal Veterinary College in London. Gray*, who was then in charge of the Veterinary Department of Southern Rhodesia (now Zimbabwe), recruited Bevan to head a bacteriological institute there. Bevan arrived in the territory in 1905 and during the next three decades produced about 40 scientific papers. In December 1905 he married Violet Soulen Mary Land in Cape Town.
In 1907 Bevan published a "Preliminary report on so-called stiff sickness or three-day sickness in Rhodesia" (Journal of Comparative Pathology and Therapeutics), in which he reported a number of outbreaks of the disease (also known as ephemeral fever) in the north-western parts of the territory. However, it was not a new disease, as it was recognised by the older native inhabitants. He published a second paper, "Ephemeral fever", in the Veterinary Journal in 1912. Meanwhile, however, he realised that the facilities for research were poor and that he had to do field work as well. He therefore resigned in 1908 and for some time worked at the Pasteur Institute in Paris.
Around 1910 Bevan returned to Southern Rhodesia and was appointed as government veterinary bacteriologist, although adequate research facilities became available only from 1922. He spent most of his career doing research on trypanosomiasis (Nagana), on which he read a paper in 1911 before the South African Association for the Advancement of Science. The paper was published in the association's Report (pp. 135-149) for that year. However, he found time also to investigate several other diseases. In 1912, a year after blackquarter in cattle was first noted in Southern Rhodesia, he published a paper on this disease in which he compared it to a disease of sheep in England known as "struck". That same year he described "The anaplasmosis of cattle" (tick-borne gall sickness) in the Veterinary Journal. Still in 1912 and in 1913 he produced two papers, both published in the Veterinary Journal, on bovine piroplasmosis (redwater) in Southern Rhodesia and the effectiveness of immunising imported cattle against it.
In 1911 Bevan published a paper on "The transmission of horse-sickness through the dog by feeding" in the Agricultural Journal of Southern Rhodesia. Further experiments that year confirmed that the disease could be transmitted from horses or mules to dogs that ate the meat of infected animals, and to horses again by injections of blood. It is recorded that Bevan produced a horsesickness vaccine based on virus attenuated by passage through dogs. This vaccine was used in the territory until 1932.
In 1921 Bevan was appointed as the first Director of Veterinary Research of Southern Rhodesia, stationed in Salisbury (now Harare). During the next few years he published two papers on contagious abortion in cattle (brucellosis). In the first of these, "Infectious abortion of cattle and its possible relation to human health", published in the Transactions of the Royal Society of Tropical Medicine and Hygiene (1922), he was the first to suggest that the disease can spread from cows to humans. His views were soon confirmed, when Orpen in 1924 found that the strains of the bacterium Brucella abortus extracted from affected cows and humans were identical.
By 1910 Bevan was a member of the South African Association for the Advancement of Science. He retired to Pinelands, Cape Town, where he died in 1957.