We report the discovery of WASP-26b, a moderately over-sized Jupiter-mass exoplanet transiting its 11.3-mag early-G-type host star (1SWASP J001824.70-151602.3; TYC 5839-876-1) every 2.7566 days. A simultaneous fit to transit photometry and radial-velocity measurements yields a planetary mass of 1.02+/-0.03M_{Jup} and radius of 1.32+/-0.08R{Jup}_. The host star, WASP-26, has a mass of 1.12+/-0.03 and a radius of 1.34+/-0.06 and is in a visual double with a fainter K-type star. The two stars are at least a common-proper motion pair with a common distance of around 250+/-15pc and an age of 6+/-2Gy.