Born in Orange, New Jersey in 1949 Whelan grew up in Livingston, New Jersey. In 1973 he graduated with honors with a BA in history from Blackburn College in Carlinville, Illinois.
In 1979 Whelan received an MA in history from the University of Missouri at Columbia, Missouri. From 1979 to 1981 he was the assistant state archivist for the State of Missouri.
Whelan was a feature writer with the Morning Call newspaper in Allentown from 1981 to 2006 where he wrote over 2000 articles, many on local history. He was the historian in residence, and director of community outreach and special projects at the Lehigh County Historical Society from 2006 to 2009.
Whelan has written five books on Lehigh Valley history that include "Harry C. Trexler: His Life and Legacy." He is the co-author with Kurt D. Zwikl of "Hess's Department Store." The book, currently in its fourth printing, is a part of Arcadia Press's Images of America series.
Whelan also served as on-air historian for PBS 39's documentary, "Hess's: Hollywood on Hamilton Street." Whelan is currently researching a wide variety of historical topics pertaining to local history.