Two new non-centrosymmetric ternary compounds, MgSiAs2 and Mg3Si6As8, are discovered via metal flux and solid-state synthetic methods. MgSiAs2 belongs to the well-known II-IV-V-2 family, which is extensively studied experimentally and computationally for their optical properties. MgSiAs2 is computationally predicted but not experimentally known prior to this work. Mg3Si6As8 crystallizes in a new non-centrosymmetric cubic chiral structure type with the Pearson symbol cP68. The syntheses, crystal structure, thermal and chemical stabilities, electronic structures, and optical properties of these two new compounds are investigated in this work. Optical absorption measurements and electronic structure calculations reveal the two compounds to be direct or pseudo-direct bandgap semiconductors (1.8-2 eV). The crystal structures of both compounds are non-centrosymmetric, though Mg3Si6As8 belongs to the 432 chiral crystal class, which is optically active but does not exhibit second harmonic generation (SHG) behavior. The SHG response of MgSiAs2 is 60% of that for AgGaS2, but MgSiAs2 exhibits a higher laser damage threshold than AgGaS2 at 33.2 MW cm(-2).