Pope Leo X created him cardinal deacon in the consistory of 1 July 1517 at the age of sixteen with the deaconry of SS. Vito e Modesto.[1] Later his uncle appointed him administrator of the see of Orvieto on 24 August 1520 and he kept that post until 3 September 1529. Ridolfi participated in the conclaves of 1521–1522 and 1523.
Ridolfi was administrator of Forlì (16 April 1526 - 7 August 1528). During the Sack of Rome (1527) he was taken hostage to Hugo of Moncada with other cardinals. Later he was named administrator of Viterbo (16 November 1532 – 6 June 1533), administrator of the metropolitan see of Salerno (7 February 1533 - 19 December 1548) and administrator of Imola (4 August 1533 - 17 May 1546). Pope Clement VII opted him for the deaconry of Santa Maria in Cosmedin on 19 January 1534.[1] He participated in the Papal conclave, 1534.
Pope Paul III appointed him administrator of Viterbo again (8 August 1538 - 25 May 1548) and opted him for the deaconry of Santa Maria in Via Lata on 31 May 1540 as he became cardinal protodeacon. He was a member of a special commission of eleven cardinals for reform of the Roman Curia. On 8 January 1543 he was named Archbishop of Florence for second time and resigned again on 25 May 1548.
A patron of the arts, Ridolfi had an extensive collection of books, paintings, and sculpture that passed to his brother Lorenzo.[3] A large armorial pitcher, currently held by the Metropolitan Museum of Art is believed to have been commissioned by Ridolfi on the occasion of Charles V's coronation in Bologna in 1530.[4]
Byatt, Lucinda M. C. (1988). "The concept of hospitality in a cardinal's household in Renaissance Rome". Renaissance Studies. 2 (2): 312–320. doi:10.1111/j.1477-4658.1988.tb00159.x. JSTOR24409406. [very tangential, of background value only]
[1] Una suprema magnificenza :Niccolo' Ridolfi a Florentine Cardinal in sixteenth-century Rome, by Lucinda Byatt, Ph.D. thesis, European University Institute, 1983.
Ridolfi, Roberto (1929). "La biblioteca del cardinale Niccolo Ridolfi (1501-1550)". La Bibliofilia. 31: 173–193.