He joined The Register in 1861 and became head reporter 1866, a proprietor in 1877 and editor in 1878, succeeding John Howard Clark, resigning in 1899 due to ill-health. He was then appointed resident reporter in Britain until retiring and returning to Adelaide in 1908, dying 7 years later. As an editor he was an outspoken supporter of female suffrage, free secular education, free trade between the Colonies, and Federation.
Finlayson was an active Congregational churchman and was appointed Justice of the Peace in 1880.
In 1878 Finlayson built a residence "Strelda" in North Adelaide which still stands, at 217-221 Stanley Street. Finlayson was born at "Helenholm", Mitcham, South Australia.
Finlayson married Alice Shoobridge (ca 1847 – 6 June 1933) on 20 March 1878.