A new baryon state is observed in the Λ 0 b π + π − mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies √ s = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb −1. The mass and natural width of the new state are measured to be m = 6072.3 ± 2.9 ± 0.6 ± 0.2 MeV , Γ = 72 ± 11 ± 2 MeV , where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Λ 0 b baryon mass. The new state is consistent with the first radial excitation of the Λ 0 b baryon, the Λ b (2S) 0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λ b (5912) 0 and Λ b (5920) 0 states are also reported.