The second son of South Australia pioneers Robert and Mary Thomas, William Kyffin Thomas was born in London and apprenticed to a printer, before migrating at the age of fourteen to Adelaide with his family. William became overseer of his father's printing office, Robert Thomas and Co. This firm produced the colony's first newspaper, the South Australian Gazette and Colonial Register, between 1836 and 1842, when the company became insolvent and the paper was sold to a rival newspaper. William Kyffin Thomas was employed to manage the paper from 1850, and in May 1853, with a number of associates, managed to buy it back, at the same time purchasing the the Adelaide Observer. He became principal proprietor of the company, named W. K. Thomas & Co. William's son, Robert Kyffin Thomas took over his share of the business in 1877, a year before his father's death.
William's mother Mary Thomas documented the story of the Thomas family and the Register in her diaries and letters, published in 1915 as The Diary and Letters of Mary Thomas (1836-1866).
