The two-loop self-energy correction is evaluated to all orders in Zα for the ground-state Lamb shift of H-like ions with Z≥10, where Z is the nuclear charge number and α is the fine-structure constant. The results obtained are compared with the analytical values for the Zα-expansion coefficients. An extrapolation of the all-order numerical results to Z=1 is presented and implications of our calculation for the hydrogen Lamb shift are discussed.