The structural and magnetic properties of M2IrSi (M=Ti, Cr and Mn) full-Heusler compounds were investigated using WIEN2k program. The ferromagnetic states (FM) were compared to the non-magnetic states in the Hg2CuTi and Cu2MnAl structures to determine more stable state as energetically using the optimization curves. For all compounds, FM states are the most stable states in the Hg2CuTi type structure. The electronic calculations show that the majority electrons of Ti2IrSi, Cr2IrSi and Mn2IrSi compounds have metallic feature. For Ti2IrSi and Mn2IrSi compounds, the minority electrons have semiconducting nature with an energy gap of 0.89 and 0.41 eV, respectively. Finally, Ti2IrSi compound is a conventional half-metallic, Cr2IrSi compound is metallic and Mn2IrSi is a half-metallic ferromagnet within 2.73,1.0 and 3.0 mu B/f.u. magnetic moment, respectively.