McKellar's son, Patrick, said his father died Thursday at Ocean Springs Hospital after a brief illness.
A memorial service is Monday at 11 a.m. at St. John's Episcopal Church in Ocean Springs.
McKellar worked from 1972-76 for Waller, who died last November. McKellar most recently served as editor and publisher of the weekly Ocean Springs Record. McKellar left the newspaper last year and recently completed his first work of fiction, "The Candidate Conspiracy," due out this month. He was preparing a book tour when he became ill.
Survivors include his son Patrick and a daughter Catherine and four grandchildren.