It is either the Anglicized form of Ó Cadhla or a variant of Keeley. Notable people with the surname are:Benedict Kiely (1919–2007), Irish writer and broadcaster
Dan Kiely, Irish auctioneer and politician
David M. Kiely, Irish writer
Text adapted from Wikipedia, CC BY-SA 4.0. Photograph: Max Surprenant (see Commons), Wikimedia Commons.