Niccolò became a long time friend of humanist Gian Giorgio Trissino, who served Leo as his Nuncio in Germany.
[1] Pope Leo X created him cardinal deacon in the consistory of 1 July 1517 at the age of sixteen with the deaconry of SS.
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.
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.