Eugenio Pacelli, was Camerlengo, when elected as Pius XII (#261) on March 2, 1939 — which happened to be his 63 birthday. (As far as I can see, going back to 1400, he is the only pope elected on his birthday).
He was the third presiding Camerlengo to be elected pope. Leo XIII (#257), in February 1878, was also the Camerlengo at the conclave that elected him. Prior to that it was Innocent VII (#205) in 1404.
Those were the only three presiding Camerlengos to be elected pope.
Honorius III (#178) and Alexander IV (#182) had been Camerlengos but not at the time they were elected.
Typically, WHY we haven’t seen more Camerlengos elected pope is because they are usually too closely aligned with the prior pope.
This quick post is in reply to a question I got this morning.
This information is on Page 42 of my ‘The Next Pope‘ book. [[ smile, smile ]].