For centuries, when a man has been elected pope he was already a cardinal of the Catholic Church. However, Church law does not require that an elected pope be a cardinal first and, in fact, that has not always been the case.
The eligibility requirements to be selected as pope are implicitly pretty simple: the future pope must be a baptized Catholic man. At least for the last 500 years, the future pope has also been a cardinal, in our modern understanding of the term. But there are a few times in Church history when that hasn’t been true.
Take Pope John XIX, elected in 1024, who was a “Cardinal-Deacon,” but not a bishop or even a priest. He was actually a consul and a senator when elected. He was a controversial pope for having little experience within the Church and was hurriedly ordained before taking on the papacy.
Pope Gregory X was elected in 1271 when he was a bishop - but not cardinal. He was in the Holy Land on a crusade and had to make the trip back to Rome.
Or consider Pope Celestine V who was a hermit monk who really didn’t want to accept the papacy, but did in 1294. He actually didn’t last long - he voluntarily abdicated after only five months and became famous in our own times because Pope Benedict XVI visited his tomb before himself resigning. When Pope Francis did the same thing, much speculation ensued.
Cardinals are kinda new
It is worth noting that the status of a cardinal wasn’t really codified until the 11th century. The term cardinal evolved from being a designation of a clergy member who had a certain sort of seniority or importance, into the understanding of cardinals we have today. This was cemented in the Decree of 1059 A.D. Concerning Papal Elections.
In the early Church particularly, there were priests who became pope. There were even popes who were married, though tradition holds that they practiced clerical celibacy.
First on this list is Peter the Apostle, whom we know was married because Scriptures tell us that Jesus healed his mother-in-law.
The likelihood of anyone but a cardinal being elected today is very low. Then again, we hadn’t seen a pope resign like Pope Benedict XVI did in a very, very long time, so never say never!
Cardinal or not, the pope will be announced to the universal Church with a resounding “Habemus Papam” (We have a Pope!)
