He was also appointed President of the archives and Commissary of the papal army during the Wars of Castro.

In July 1643 Rappaccioli was elevated to cardinal by Pope Urban VIII, was made papal legate to the Province of Viterbo and Cardinal-Priest of Santa Maria in Via Lata.

On 28 Oct 1646, he was consecrated bishop by Marcantonio Franciotti, Cardinal-Priest of Santa Maria della Pace, with Alfonso Gonzaga, Titular Archbishop of Rhodus, and Girolamo Farnese, Titular Archbishop of Patrae, serving as co-consecrators.

[2] In 1650 he was appointed Cardinal-Priest of Santa Cecilia in Trastevere while retaining administration of the diocese of Terni.

He participated in the conclave of 1655 which elected Pope Alexander VII and became Camerlengo of the Sacred College of Cardinals between 1656 and 1657.