Landscape context is a strong predictor of species persistence, abundance and distribution, yet its influence on the success of ecological restoration for mammals remains unclear. Thus, a primary question arises: which landscape size best predicts the effects of forest cover on restoration success? To answer this, we conducted a global meta-analysis for mammals. Response ratios were calculated for comparisons between reference (e.g. old-growth forest) and disturbed sites (degraded or restored). Using an information-theoretic approach, mean response ratio (restoration success) and response ratio variance (restoration predictability) within each study landscape were regressed against the percentage of overall (summed forest cover) and contiguous (summed pixels of ≥ 60% forest cover) forest within eight different buffer sizes of radius 5–200 km (at 1 km resolution). The best buffer (landscape) size varied for: (i) overall and contiguous forest cover, and (ii) mean response ratio and response ratio variance. Mammals were influenced by contiguous forest cover only (5, 10 and 50–200 km radii). Overall, mean response ratio and response ratio variance were positively and negatively non-linearly related with both overall and contiguous forest cover, respectively. We reveal for the first time a clear pattern of increasing restoration success and decreasing uncertainty as contiguous forest cover increases. We also indicate preliminary recommended buffer sizes for investigating landscape restoration effects on mammals. When setting targets for ecological restoration, policymakers and restoration practitioners should account for: i) the landscape context, and ii) the uncertainty in restoration success, as it increases when contiguous forest cover falls below about 50%.