Hincmar was born in 806 to a distinguished family of the West Franks. Destined to the monastic life, he was brought up at Saint-Denis under the direction of the abbot Hilduin (died 844), who, went appointed court chaplain in 822, brought him to the court of the emperor Louis the Pious. There he became acquainted with the political as well as the ecclesiastical administration of the empire. When Hilduin was disgraced in 830 for having joined the party of Lothair I, Hincmar accompanied him into exile at Corvey in Saxony. Hincmar used his influence with the emperor on behalf of the banished abbot, and not without success: for he stood in high favour with Louis the Pious, having always been a faithful and loyal adherent. He returned with Hilduin to Saint-Denis when the abbot was reconciled with the emperor and remained faithful to the Louis during his struggle with his sons.
After the death of Louis the Pious (840) Hincmar supported Charles the Bald (see Capitularies of Charles the Bald), and received from him the abbacies of Nôtre-Dame at Compiègne and Saint-Germer-de-Fly.
Archbishop Ebbo had been deposed in 835 at the synod of Thionville (Diedenhofen) for having broken his oath of fidelity to the emperor Louis, whom he had deserted to join the party of Lothair. After the death of Louis, Ebbo succeeded in regaining possession of his see for some years (840-844), but in 844 Pope Sergius II confirmed his deposition. In 845 Hincmar obtained through the king's support the archbishopric of Reims, and this choice was confirmed at the Synod of Beauvais (April 845). He was consecrated archbishop on 3 May 845; in 847 Pope Leo IV sent him the pallium.
One of the first cares of the new prelate was the restitution to his metropolitan see of the domains that had been alienated under Ebbo and given as benefices to laymen. From the beginning of his episcopate Hincmar was in constant conflict with the clerks who had been ordained by Ebbo during his reappearance. These clerks, whose ordination was regarded as invalid by Hincmar and his adherents, were condemned in 853 at the Council of Soissons, and the decisions of that council were confirmed in 855 by Pope Benedict III.
This conflict, however, bred an antagonism of which Hincmar was later to feel the effects. During the next thirty years the archbishop of Reims played a very prominent part in church and state. His authoritative and energetic will inspired, and in great measure directed, the policy of the West Frankish kingdom until his death.