We report the discovery of a 7.3 MJ exoplanet WASP-14b, one of the most massive transiting exoplanets observed to date. The planet orbits the 10th-magnitude F5V star USNO-B1 11118−0262485 with a period of 2.243 752 d and orbital eccentricity e= 0.09. A simultaneous fit of the transit light curve and radial velocity measurements yields a planetary mass of 7.3 ± 0.5 MJ and a radius of 1.28 ± 0.08 RJ. This leads to a mean density of about 4.6 g cm−3 making it the densest transiting exoplanets yet found at an orbital period less than 3 d. We estimate this system to be at a distance of 160 ± 20 pc. Spectral analysis of the host star reveals a temperature of 6475 ± 100 K, log g= 4.07 cm s−2 and v sin i= 4.9 ± 1.0 km s−1, and also a high lithium abundance, log N(Li) = 2.84 ± 0.05. The stellar density, effective temperature and rotation rate suggest an age for the system of about 0.5–1.0 Gyr.