The September 1590 papal conclave, attended by 54 cardinals, elected Cardinal Giovanni Battista Castagna as Pope Urban VII.

[1][2] The conclave lasted a week, and was heavily swayed by the influence of the twenty-two Spanish cardinals.

[3][4][2] Castagna, who had been favored by Sixtus V as a successor and was on the list of candidates whom Philip II of Spain had approved, was a favorite from the beginning,[1][2][5] although a significant opposing faction supported Marco Antonio Colonna.

[1][6] Castagna's poor health, which would ultimately kill him after a papacy of only thirteen days, made him a more palatable candidate to cardinals who were outraged at Philip's attempts to sway the election.

[2] Contemporary newspapers reported that a disagreement between Cardinals Ascanio Colonna and Francesco Sforza di Santa Fiora during the conclave nearly became violent.