His time there saw him cover the court case of the last man to be executed in Leicester Prison and interview the likes of Louis Armstrong.
Denis had joined the Mercury from a weekly newspaper in Yorkshire in 1949.
Retired Mercury assistant editor Terry Dwyer said: “It was my privilege to have known Denis as a friend and colleague during most of his long career at the Mercury.
“My abiding memory is of Denis as a senior reporter when I joined the Mercury newsroom as a trainee journalist in 1951. Some of us beginners were lucky enough to have had Denis as our mentor.
“He was an instantly likeable man with an enthusiasm for his work which rubbed off on me. What immediately struck me was the regard in which he was held.
“Denis would have laughed at any thought of his being regarded as a ‘role model’ but I owe him much for the standards he set, for his advice and encouragement in those early days and, not the least, for a friendship that lasted beyond our respective retirements.”
His daughter Rosie Thomas added: “He was larger than life, witty and generous. No-one disliked him.
“He was compassionate, principled and would talk to a dustman and a duke just the same. He was a man of the people.”
Denis is survived by wife, Peggy, children Stephen, Martin, Rosie Thomas and Helena Edwards, seven grandchildren and five great-grandchildren.