John Mackinnon Robertson PC (14 November 1856 – 5 January 1933) was a prolific journalist, advocate of rationalism and secularism, and Liberal Member of Parliament in the United Kingdom for Tyneside from 1906 to 1918.
Robertson was born in Brodick on the Isle of Arran; his father moved the family to Stirling while he was still young, and he attended school there until the age of 13. He worked first as a clerk and then as a journalist, eventually becoming assistant editor of the Edinburgh Evening News.
He wrote in February 1906 to a friend that he "gave up the 'divine'" when he was a teenager. His first contact with the freethought movement was a lecture by Charles Bradlaugh in Edinburgh in 1878. Robertson became active in the Edinburgh Secular Society, soon after. It was through the Edinburgh Secular Society that he met William Archer and became writer for the Edinburgh Evening News. He eventually moved to London to become assistant editor of Bradlaugh's paper National Reformer, subsequently taking over as editor on Bradlaugh's death in 1891. The National Reformer finally closed in 1893. Robertson was also an appointed lecturer for the freethinking South Place Ethical Society from 1899 until the 1920s.
An advocate of the "New Liberalism," Robertson's political radicalism developed in the 1880s and 1890s, and he first stood for Parliament in 1895, failing to win Bradlaugh's old seat in Northampton as an independent radical liberal. Robertson was a staunch free trader and his Trade and Tariffs (1908) "became a bible for free-traders pursuing the case for cheap food and the expansion of trade".