[2] He graduated from the University of Bologna with a degree utroque iuris in both canon and civil law.
He was sent as nuncio to the court of François I to negotiate peace and to agree on the celebration of a general council, June 1543 to May 1544.
[3] in the meantime he was again nuncio in France, charged with opposing royal support of Protestantism at the court of the new king, Henri II, July 1546 to September 1547.
As legate to Emperor Charles V he negotiated the continuation of the Council of Trent and obtained assistance for the war of Parma and Mirandola.
Dandini was created cardinal by Pope Julius III, in the consistory of 20 November 1551, and was made cardinal-secretary of state, to fill the post of the incompetent cardinal-nephew Innocenzo Ciocchi del Monte.