Born in 1903 in Baltimore, Mackie studied civil engineering at Union College in Schenectady, New York. In 1934 he went to work for Du Pont in construction and retired in 1968 as manager of construction. "They called me manager, now they call them directors. They give them a big title, but they gave me more money, "he said. After the war, Mackie was construction manager at Savannah River, the plant in South Carolina built by Du Pont in the early 1950s to produce material for hydrogen bombs.