EWTN Catholic Q&A
Has an elected Cardinal every declined?
Question from Elena Dwyer on 04-17-2005:

One of my students asked if anyone has ever declined the Papacy after having won the election. Is there any knowledge or record of that every happening? Thank you.

Answer by David Gregson on 04-19-2005:

There is a story that Gregory the Great (who reigned 590-604) fled from Rome when he was elected, and hid in the forest for three days before he accepted the papacy. But it's probably just a legend. There may have been examples where men elected have declined, but I don't know who they might be. Since conclaves have been secret, no cardinal taking part would be allowed to reveal it.