Griffith Evans was born on August 7, 1835, in Towyn, Merionethshire, Wales.

He was a Welsh microscopist, bacteriologist, and pioneer of protozoon pathology. In 1855, he graduated from the Royal Veterinary College as M.R.C.V.S. and became a veterinary surgeon in the Royal Artillery in 1860. He went to Canada with troops and was stationed at Montreal in 1861. He graduated from McGill University medical faculty in 1864. The subject of his graduation thesis was “Tuberculosis”; he gave evidence of its infectious nature and advocated open-air treatment. He returned with troops to England in 1870. In 1877, he was posted to India where he investigated diseases fatal to cavalry and artillery horses and camels. He was able to prove that the disease was caused by microbes in the blood; these have been given his name as "Trypanosoma Evansi". He returned to Britain in 1885 and in 1890, he retired from the Army with the rank of inspecting veterinary surgeon. He settled in Brynkynallt, Bangor, where he became a lecturer at the University College's Agricultural Department until 1910. In 1917, he was awarded the Mary Kingsley medal and the honorary degree of D.Sc. in 1919.

In 1870, he married Catherine Mary Jones (1843-1923). He died on December 7, 1935, in Bangor, Denbighshire, Wales.