During the 1850s he teamed up with Henry Edwards, a famous stage actor. The two travelled widely throughout the colony, enjoying the bush environment. A shared passion for entomology, particularly for Lepidoptera and Coleoptera (butterflies, moths and beetles), saw large collections expertly preserved and meticulously documented.
Kershaw's skills brought him to McCoy's attention, and in 1856 he was offered a temporary position as taxidermist at the National Museum. By 1860 he gained permanent employment as an assistant to McCoy, and in 1864 he was promoted to second taxidermist, ultimately retiring in 1891.
McCoy held Kershaw in high regard. In Decade 20 of the Prodromus the Australian Painted Lady Butterfly, Vanessa kershawi, was described by McCoy and dedicated to: 'my excellent friend, William Kershaw, the senior taxidermist at the Melbourne Museum, who made our singularly fine and extensive local collection of the Insects of Victoria, and whose unequalled knowledge of the habits and distribution of the habits and distribution of our Insects, and extraordinary zeal and devotion to his duties as my assistant in this branch of the Museum.'
Kershaw died at Prahran on 18 October 1899. This was the same year as McCoy's death, the Museum's relocation to the city site, and probably also when Kershaw's whale skeleton was removed from the University grounds.
