The first heptacoordinate cobalt catalyst for light-driven hydrogen production in water has been synthesized and characterized. Photochemical experiments using [Ru(bpy)(3)](2+) as photosensitizer gave a turnover number (TON) of 16300molH(2)(molcat.)(-1) achieved in 2hours of irradiation with visible (475nm) light. This promising result provides a path forward in the development of new structures to improve the efficiency of the catalysis.