Bentley Mackay was born in 1894 in Hope Villa, Louisiana. Records indicate he did not have a college degree, but completed agriculture and journalism courses under another AAACE president, Marvin Osborn.
He joined the LSU agricultural extension service in 1920 as editor of publications. In 1935, he took a three-year leave of absence from LSU to head the field information office of the U. S. Department of Agriculture's Agricultural Adjustment Administration in Washington. He was responsible for the southeastern states. In 1938 he resumed his duties as agricultural extension editor at LSU. In 1941, he joined the information staff of the USDA in Washington as southern regional director of all USDA information programs.
In 1944, he was appointed agricultural reporter and adviser to the American embassy at Recife, Brazil. He returned to LSU in 1946 to become publicity director of the rodeo and livestock show, a position he held until 1960, when he retired from LSU to become editor for the Council on the Aging.
In addition to AAACE, Mackay was a member of the American Legion and Sigma Delta Chi. He died at Hope Villa December 16, 1975 at the age of 81.