An integrated approach is used to study the local structure and molecular mobility in the ternary system LiNO3–NaNO3–H2O. Coefficients of self-diffusion are measured via NMR on 1H and 7Li nuclei for a binary aqueous solution of LiNO3 and two series of a ternary solution. It is found that when 0.5 mol/kg NaNO3 is added, the mobility of lithium cations and water molecules is virtually the same as in the binary solution of LiNO3. This effect is studied by means of molecular dynamics. The structure of the solution at the molecular level is considered in detail with quantitative analysis of variants of the composition of the solvate shells of ions. It is established that adding NaNO3 salt to the lithium solution in the considered range of concentrations has a fairly weak effect on the solvation of lithium cations. When 0.5 mol/kg NaNO3 is added, the local environment of the lithium cation is virtually the same as the one in the binary solution of LiNO3, and the resulting excess of nitrate anions is predominantly redistributed to structures formed in the local environment of sodium cations.