The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-β (0νββ) decay of Ge76, whose discovery would have far-reaching implications in cosmology and particle physics. By operating bare germanium diodes, enriched in Ge76, in an active liquid argon shield, GERDA achieved an unprecedently low background index of 5.2×10-4 counts/(keV kg yr) in the signal region and met the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of 0νββ decay in Ge76 is set at T1/2>1.8×1026 yr at 90% C.L., which coincides with the sensitivity assuming no signal.