He was one of the closest collaborators of Cardinal Alessandro Farnese, both as Bishop of Parma and afterwards when he became Pope Paul III.

He served the pope as Vicar of Rome, and Prefect of the Tribunal of the Signature of Justice, as well as a member of several ad hoc commissions of cardinals.

[3] Finally, through the influence of Felinus Sandaeus, a jurisconsult and Auditor of the Rota, he obtained a position in the household of Cardinal Franciotto Galeotto della Rovere, the nephew of Pope Julius II.

[5] At Rome, he entered the household of Cardinal Alessandro Farnese, seniore, the future Pope Paul III.

[11] On the election of Cardinal Farnese as Pope Paul III on 13 October 1534, Guidiccioni was sent by the city of Lucca to Rome as one of the members of its congratulatory embassy.

Guidiccioni wrote to the Pope, Luca vale, revocat nos marcia curia, Paulus sic iubet, en iussus non rediturus.

[16] On 23 July 1536, he was appointed, along with Cardinals Sadoleto, Cortese, Fregoso, Giberti and Carafa, to make preparations for the council.

[20] One week after he was named Bishop of Teramo, the pope made him a cardinal priest in the consistory of 19 December 1539.

He was a dissenting voice on the congregation, questioning whether yet another religious order was needed or appropriate, and whether it might lead to strife rather than harmony.

[23] But after the pope issued the papal bull Regimini militantis Ecclesiae approving the order, Cardinal Guidiccioni became a strong supporter.

[1] On 17 February 1540, Pope Paul III named Cardinal Guidiccioni to the office of Prefect of the Signature of Justice (a court of appeal in the Roman Curia).

[1] On 21 July 1542, following the issue of his Bull Licet ab initio, Pope Paul named six cardinals, Gian Pietro Carafa, Juan Alvarez de Toledo, Pier Paolo Parisio, Bartolommeo Guidiccioni, Dionisio Laurerio, and Tommaso Badia inquisitors general of the Roman Inquisition.

[29] He finally received episcopal consecration from the hands of Cardinal Rodolfo Pio da Carpi in the Sistine Chapel on 28 August 1546,[1] with Cristoforo Spiriti, Bishop of Cesena, and Giovanni Giacomo Barba, Bishop of Teramo, serving as co-consecrators.

[32] Cardinal Guidiccioni died in Rome on 4 November 1549, six days before the death of his friend Paul III.