Tomkinson was born in
Denbighshire, Wales, and served as a clerk in a Liverpool shipping office, before working in the North and South Wales Bank, first as teller, and rapidly rose through the ranks to become Director. In 1850 he accepted the position of Manager of the
Bank of Australasia in Sydney. In 1851 he transferred to Adelaide, replacing Marshall Macdermott, whose daughter he married in 1853. They initially lived on King William Street, but sometime before 1860 acquired "Mangona" at 9 Blackburn Drive,
Crafers, close to Summit Road,
Mount Lofty, which became their summer residence and later, as "St Barberie" owned by
C. T. C. de Crespigny and family. Around the time he arrived in Adelaide, the gold rush to Victoria was underway, and South Australia was undergoing a crisis brought about by shortage of currency to pay for the gold being brought back to the Colony. Moves were made for the creation of a South Australian gold coinage, led by
George Tinline. This was strenuously opposed by Tomkinson in representations to the Legislative Council. He retired from the bank in October 1879. ==Other interests==