A two-dimensional, steady-state, laminar, double-diffusive convection within the rectangular cavity containing heated rectangular blockage at its geometric center has been explored by the lattice Boltzmann method. The research work is focused on determining the combined influence created by a magnetic force and double-diffusive convective characteristics in the shallow cavity (length > height) and rectangular blockage (width > height). In particular, the influence of various pertinent parameters, such as the aspect ratio of the cavity (AR = 1, 2, and 4), the aspect ratio of the heated blockage (ar = 1, 2, and 4), Lewis number (Le = 2, 5, and 10), Prandtl number (Pr) = 0.054, Rayleigh number (Ra = 103, 104, and 105), Hartmann number (Ha = 0, 50, and 100), and the buoyancy ratios (N = -2, 0, and 2), on the double-diffusive convection accompanied by magnetohydrodynamics characteristics has been elaborated. The working fluid in the cavity is considered to be a liquid metal-sodium-potassium alloy (Pr = 0.054). The results indicated the augmentation in Le leads to the formation of multi-cell zones within the cavity. For N < 0, the direction of fluid flow, thermal, and concentration patterns is reversed as for N > 0. Denser crowding of temperature and concentration contour lines along the block was noticed for N = 2 than N = -2 for a given Ra. The total Nusselt (Nutotal) and Sherwood number (Shtotal) decreases with a decrease in N. The heat and mass transfer rates enhance with augmentation in both cavity and blockage aspect ratios. © 2022 Author(s).