In this study, by using full-potential linearised augmented plane wave (FP-LAPW) method with the generalised gradient approximation (GGA) based on density functional theory (DFT), the structural, electronic, elastic and magnetic properties of the Heusler alloys Cr$_2$NbSi$_{1−x}$Ge$_x$ have been evaluated. The AlCu$_2$Mnl-type structure is more stable than the CuHg$_2$Ti-type structure at equilibrium volume for the compounds. The ground-state properties of our alloys including the lattice parameter and bulk modulus were calculated. In view of Poisson’s and Pugh’s ratio, the ductility and brittleness of Cr$_2$NbSi$_{1−x}$Ge$_x$ has been analysed. The mechanical stability is maintained throughout the pressure range with high value of Debye temperature. The electronic band structures and density of states of our compounds show a half metallic character with total magnetic moments, −3.00 $\mu$B per formula unit with indirect band gap, $E_{g} = 0.152$ eV and 0.262 eV for Cr$_2$NbSi and Cr$_2$NbGe respectively. Furthermore, we have analysed the thermal properties by the quasi-harmonic Debye model. Through the obtained results, we can say that these compounds can be strong candidates for future spintronic applications.