With over 6,600 described species, harvestmen represent a morphologically and ecologically diverse group of arachnids with a cosmopolitan distribution. Although members of the order Opiliones are believed to have been among some of the earliest terrestrial arthropods, the Palaeozoic fossil record of harvestmen is sparse. Herein, a new harvestman, Devonopilio hutchinsoni gen. et sp. nov., is described based on a penis preserved in Lower Devonian Rhynie chert from Aberdeenshire, Scotland (Pragian, ca. 407 Ma). Together with Eophalangium sheari, another Early Devonian harvestman known from the Rhynie chert, the new species represents the earliest member of the order Opiliones in the fossil record and one of the oldest terrestrial animals. The new species differs significantly from E. sheari in penis morphology, indicating that harvestmen began to diversify before the Early Devonian.