Arnulf (also Arnulph or Arnoul) was archbishop of Reims and the illegitimate son of King Lothair of France.
Archbishop Adalberon wanted Gerbert of Aurillac to succeed him, but King Hugh Capet accepted the elected Arnulf, a Carolingian, in March 989. In September of that year, Arnulf supported an attempt to place his uncle Charles, duke of Lower Lorraine, on the throne. Charles briefly held Rheims and Laon. In 990, Arnulf refused to attend a synod at Senlis and he and Charles were imprisoned (March 29).
In June, 991, Seguin, Archbishop of Sens presided over a Synod of Reims in the Basilica of Saint Basle, which deposed Arnulf for alleged high treason in favour of Gerbert, later Pope Sylvester II.
This deposition was much opposed, however. Pope John XV sent Leo, abbot of Saints Boniface and Alexius at Rome, as legate to preside over a synod at Mouzon, June 2, 995. Gerbert was suspended from the episcopum. A second synod, held July 1, declared the whole process of deposition and elevation to be illegal and invalid. Thus, Arnulf was reinstated.
He crowned Hugh, the son of Robert II, co-king in the Capetian tradition in 1017. At this time, any resistance to the new dynasty had died in him.