Process for gasifying an organic material, comprising the following steps: subjecting an organic material to a drying phase to reduce its humidity content and obtain dry organic material and steam, and extracting said steam; subjecting the dry organic material to pyrolysis and generating a pyrolysis gas and a carbonaceous solid residue from the dry organic material, the pyrolysis gas containing a tar fraction; separating the pyrolysis gas from the carbonaceous solid residue, wherein separating the pyrolysis gas comprises extracting the pyrolysis gas and conveying it separately from the carbonaceous solid residue generated by the pyrolysis; subjecting the pyrolysis gas to a thermochemical treatment; and, after the thermochemical treatment, causing the treated pyrolysis gas to penetrate through a reducing bed (31) composed of the carbonaceous solid residue generated by the pyrolysis, and producing a synthesis gas. Subjecting the pyrolysis gas to a thermochemical treatment comprises: subjecting the pyrolysis gas to a first combustion with a gasifying agent under sub-stoichiometric conditions by using ejecting nozzles (25) arranged below and upstream of the reducing bed (31), and obtaining the cracking of the tar fraction contained in the pyrolysis gas; and subjecting the pyrolysis gas to a second combustion introducing an additional gasifying agent in a chamber (20″) arranged above and downstream of the ejecting nozzles (25) and upstream of an interface (23) separating the chamber (20″) from the reducing bed (31), and completing the combustion of the tar fraction until the pyrolysis gas is fully converted to CO2, H2O(g) and heat.