A new ultraviolet nonlinear optical (NLO) material, Pb3Mg3TeP2O14 (PMTP), has been synthesized and characterized. The chiral material exhibits a large second harmonic generation (SHG) response of 13.5 x KDP (600 x alpha-SiO2), and the shortest absorption edge (250 nm) of reported materials with a strong SHG response (>10 x KDP). PMTP has a three-dimensional crystal structure of corner-shared MgO4, PO4, and TeO6 polyhedra, which form a [TeMg3P2O14](infinity) framework. Electronic structure calculations revealed that the stereo-active lone pair on the Pb2+ cation is critical to producing the substantial NLO response and that the NLO activity is further enhanced by the presence of triply bidentate Te6+ cations found in Te-O-O-Pb rings.