We have studied the structural, dynamical, and electronic properties of liquid Li12Si7 by means of first-principles molecular-dynamics simulations. We find that the Si atoms give rise to a covalently bonded network that can be described as originating from interconnected short chains and stars. The elements of the crystal structure that survive in the liquid state are the preferential twofold Si coordination and the angle between Si bonds. The structure factor is in overall agreement with neutron-scattering data, except for a slight nonuniform shift of peak positions. Electronic-structure calculations show that the Fermi energy is in a minimum of the electronic density of states. The resulting dc conductivity is in good agreement with the resistivity measurements by Meyer et al. Our results appear consistent with the extended Zintl principle recently proposed by Hafner and Jank.