We prepared a new binary lanthanum germanide, LaGe3, under high-pressure and high-temperature conditions (3-12 GPa, 500-1200 degrees C). It crystallizes in the BaPb3 structure (the space group R (3) over barm) with lattice constants of a = 6.376(1) angstrom, c = 22.272(3) angstrom, and V= 784.1(2) angstrom(3). We refined the structure using Rietveld analysis from X-ray powder data. The structure is composed of two types of close-packed atom layers. In one layer, every La atom is surrounded solely by Ge atoms with the same distance of 3.188 angstrom. The other layer contains Ge-3 regular, triangular cluster units with a Ge-Ge distance of 2.634 angstrom. The electron localization function and crystal orbital Hamilton population calculations suggest that the triangular cluster is composed of three Ge Ge covalent bonds and that each Ge atom has a lone pair. The temperature dependence of the magnetic susceptibility and electrical conductivity measurements revealed that LaGe3 is metallic and shows superconductivity at 7.4 K. This critical temperature is highest for the La-Ge system.