The papal conclave held on 1 and 2 March 1939 saw Cardinal Eugenio Pacelli elected on the third ballot to succeed Pius XI, who had died on 10 February, as pope.

Time magazine announced that likely contenders for the papacy included August Hlond of Gniezno-Poznań, Karl Joseph Schulte of Cologne, the Curia veteran Eugène-Gabriel-Gervais-Laurent Tisserant, Ildefonso Schuster of Milan, Adeodato Giovanni Piazza of Venice, Maurilio Fossati of Turin, and Eugenio Pacelli, a longtime diplomat in the service of the Holy See.

[4][5] On 13 February, The New York Times dismissed the idea of a non-Italian given the current state of international hostilities, though it thought Jean-Marie-Rodrigue Villeneuve of Quebec the least objectionable to the contending powers.

The five Italians remaining were Alessio Ascalesi of Naples, Giovanni Nasalli Rocca di Corneliano of Bologna, Luigi Lavitrano of Palermo, Maurilio Fossati of Turin, and Elia dalla Costa of Florence.

[6] By 20 February the paper found greater interest in the curial cardinals, Francesco Marmaggi, Massimo Massimi, and Luigi Maglione.

Pacelli, in his role as Camerlengo, announced on 10 February that the College would wait the maximum time allowed, eighteen days from the death of the pope, to start the conclave.

The time period before starting had been lengthened following the previous conclave, for which three North American cardinals had arrived too late to participate.

[4] Vincenzo Santoro, the conclave secretary, then sent a note to Vatican Radio to confirm that the smoke was white and Pacelli had been elected.

[20] At 6:06 pm,[2] the Protodeacon, Cardinal Camillo Caccia-Dominioni, made the Habemus Papam announcement in Latin from the balcony of St. Peter's Basilica.

He made only two significant changes in conclave procedures, otherwise following those established by Pope Pius X on 25 December 1904 with the constitution Vacante Sede Apostolica.