Based on ab initio calculations, we systematically investigate lanthanum monohalides [LaX (X = Cl, Br)] using generalized gradient approximation (GGA) for computation of structural and electronic properties with also test of stability by phonon dispersion curve. LaX (X = Cl, Br) are well-known layered materials exhibiting trigonal crystal structure. The structural optimization reveals LaCl and LaBr to be stable in FM1 ferromagnetic phase. The electronic properties confirm LaX to be nodal-line semimetals in FM1 ferromagnetic phase. The spin-polarized electronic band structure shows the formation of both nodal points and nodal rings at Fermi level along the first Brillouin Zone for both LaCl and LaBr. The computed positive phonon frequencies in phonon dispersion curve confirm LaCl to be stable in trigonal phase, while the negative phonon frequencies for LaBr signify their instability in trigonal phase. The present work expresses the possibility for the utilization of lanthanum monohalides belonging to the category of nodal-line semimetals for technological applications.