On 13 May 1630, he was appointed by Pope Urban VIII as Bishop of Corneto e Montefiascone. The diocese had previously been held by his uncle, Cardinal Paolo Emilio Zacchia, and then by his uncle Cardinal Laudivio Zacchia (1605–1630).[1] During the tenure of the diocese by Laudivio Zacchia, Cecchinelli served as his Vicar General in diocesan administration.[3] On 20 May 1630, he was consecrated bishop by Laudivio Zacchia, Cardinal-Priest of San Pietro in Vincoli.[2] The two cardinals and their nephew were responsible for the building of the façade of the cathedral of Montefiascone.[4]
On 4 May 1641, he was appointed by Pope Urban VIII as Apostolic Nuncio to Savoy. He resigned as Apostolic Nuncio to Savoy in April 1644.
He served as Bishop of Corneto e Montefiascone until his death on 7 March 1666. It is said that he was unsteady in his administration of justice, proceeding arbitrarily and without regard to process.[5]