Lyon Playfair was a champion of scientific and technical education who was professor of chemistry at Edinburgh University before serving as a Liberal M.P., initially for a Scottish university seat, from 1868 to 1892. This article looks mainly at his role in debates on the Education Act of 1872 and the bills which preceded it. Playfair sought to define the democratic traditions of Scottish education, especially emphasising the legacy of John Knox, and to adapt them to the new national system. He idealised the direct connection between parish schools and universities, and the opportunities available to talented boys, using newly available statistics to support his case. He also contributed to the shaping of Scottish secondary education, and to establishing the modern idea of social mobility through educational merit. When the Scottish Office was established in 1885, Playfair opposed the devolution of education and this dissent led him to move to an English seat. His career has a wider interest for the history of Scottish politics in the age of Gladstone.