A laser system for a light-pulse atom interferometer typically includes a number of laser sources for cooling and for atom optics to meet different frequency detuning requirements at different stages of a measurement sequence. The number of laser units required makes the achievable minimum size and power of the instrument challenging, especially for space applications. We demonstrate a compact cesium atom interferometer operated by only a single laser. This is achieved by dynamically changing the laser output frequency while maintaining spectroscopic reference to an atomic transition. We are able to generate cold atoms and obtain atom interferometer fringes all with the same laser.