Laymen Elected to the Papacy
Pope Saint Fabian 236
Saint Urban I
223
Noble Roman (probably a layman)
Saint Eusebius
310
Physician (most likely then a layman)
Pope Saint Eusebius: For the Catholic religion has always been preserved spotless in the Apostolic See.
John III
July 18, 560
Noble Roman
Saint Deusdedit
October 19, 615
Not even a subdeacon
John XI
March 13, 931
John was surrounded by evil men, who had raised him to authority and possessed more of it than he did. De Montor
Leo VIII
Benedict VIII
June 17, 1012
De Montor: Benedict VIII, originally named John, was a Roman, and son of Gregory, count of Tusculum, of the Conti family. Benedict was elected pope on the 17th of June, 1012; but an antipope, Gregory, soon expelled the legitimate pope.
John XX
June 6, 1024
Pope Saint Peter Celestine V
Catholic Encyclopedia Article on Papal Elections, which states: A layman may also be elected pope, as was Celestine V (1294). Even the election of a married man would not be invalid (c. "Qui uxorem", 19, caus. 33, Q. 5). ...
Pope Saint Peter Celestine was a monk. Pope Saint Siricius DZ 90: We both desire and will that monks also, whom however the authority of their manners and holy disposition of their lives and faith commend, be added to the offices of the clergy. Reading this we see that monks are not clergy.
Information is compiled from several sources, including Artaud de Montor's Lives of the Popes and the Catholic Encyclopedia