John Mackinnon Robertson was a prolific journalist, advocate of rationalism and secularism, and Liberal MP for Tyneside from 1906 to 1918.

Robertson was born on the Isle of Arran and left school at the age of thirteen to become a clerk and then a journalist. In 1878 he became a follower of secularist leader Charles Bradlaugh and became active in the secularist cause in Edinburgh, before moving 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.

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 an advocate of the Jesus-Myth theory, and in several books he argued strongly against the historicity of Jesus. According to Robertson, the character of Jesus in the New Testament developed from a Jewish cult of Joshua, whom he identifies as a solar deity. Frederick Cornwallis Conybeare wrote a book The Historical Christ directed specifically against Robertson and two other Jesus-myth advocates.