A process for ex-situ treatment of a catalyst that contains at least one hydrogenating phase, and at least one amorphous silica-alumina or a zeolite that contains acid. The process includes: a stage for introducing nitrogen by contact at a temperature that is less than 100° C., with at least one basic nitrogen-containing compound that is ammonia or a compound that can be decomposed into ammonia, the compound being introduced at a rate of 0.5-10% by weight (expressed in terms of N), and a sulfurization/activation stage with a gas that contains hydrogen and hydrogen sulfide at a temperature of at least 250° C., with this stage being carried out before or after the stage for introducing said nitrogen-containing compound, and optionally drying the catalyst that is obtained. This treatment allows a rapid, effective start-up on the hydrocracking unit.