Guido had studied under Pierre Abélard, and eventually became a distinguished master in the schools. Eventually Guido began his career in Rome as a subdeacon and a "scriptor apostolicus" under Pope Callixtus II. He was created Cardinal-Deacon of Santa Maria in Via Lata by Pope Honorius II in 1127; as such, he signed the papal bulls issued between 3 April 1130 and 21 December 1133. In the double papal election of 1130 he joined the obedience of Pope Innocent II. In December 1133 Innocent promoted him to the rank of Cardinal-Priest of San Marco. He signed the papal bulls as "S.R.E. indignus sacerdos" between 11 January 1134 and 16 May 1143. As the cardinal of San Marco's, he supported Innocent's claims with regards to Monte Cassino, and as a mark of his confidence in him, Innocent made Guido the rector of Benevento. Afterwards, he made him a papal legate to France in 1140.