The spatial distribution and atomic mobility of Li ions in the solid solution system Li1-xNb1-xWxO3 (0 less than or equal to x less than or equal to 0.5) have been studied using solid-state NMR techniques. To maintain charge balance, for each tungsten atom substituting on a niobium site, a lithium vacancy is produced in the lithium sublattice. Li-6 magic angle spinning experiments reveal multiple lithium sites, attributed to distributions of niobium and tungsten neighbors. Dipolar Li-7 second moments measured at low temperature (-100 degrees C) depend linearly on lithium content, consistent with a random distribution of vacancies. Variable temperature (-20 to 550 degrees C) Li-7 NMR studies as a function of composition give evidence for two distinct motional processes : at low temperatures (near 0 degrees C) a local hopping process involving only a minority of the lithium ions present is activated. At high temperatures (300 degrees C and above, depending on substitution levels) long-range diffusion involving all the lithium atoms is evident on the NMR time scale, As the substitution level x is increased, the long-range mobility of lithium increases. In contrast, the number of lithium atoms participating in the low-temperature process and their respective mobilities reach a maximum near x = 0.25, This result is explained on the basis of detailed simulations, considering favorable cation transport mechanisms through intrinsic vacancies of the LiNbO3 lattice. Both the Li-6 line shape and the Li-7 dynamics simulations are consistent with a statistical distribution of Nb and W atoms and formation of W-vacancy pairs along the c-axis.