We prove that, at every positive temperature, the infinite-volume free energy of the one-dimensional log-gas, or beta-ensemble, has a unique minimizer, which is the Sine-beta process arising from random matrix theory. We rely on a quantitative displacement convexity argument at the level of point processes, and on the screening procedure introduced by Sandier-Serfaty. (c) The Authors. Communications on Pure and Applied Mathematics published by Wiley Periodicals LLC.