By 1908, Mack had become general manager. Mack became president and chairman of the board in 1912, and after some years of struggle turned the failing company around. The Murphy Company improved its position during the Great Depression, and from 1929 to 1934, sales increased from $15.7 million to $28 million.
By 1934, there were 181 Murphy Company stores in eleven states and Washington, District of Columbia At one point, Murphy Company was the third-largest variety-store chain in the country.
Employee benefits included free life insurance, two weeks paid vacation, and Christmas bonuses of up to $15 in gold. Only a few Murphy stores were organized by unions, "partially because of intense antiunion campaigns mounted by management, but, more importantly, because many of G. C. Murphy"s twenty-three thousand employees didn"t feel the need for protection from a company they viewed as benevolent and even generous."
Mack enjoyed maintaining and enlarging his family farm, Old Home Manor, and frequently spent his weekends tending show horses and Black Angus cattle.
But he that to make money in a community meant to "serve its community." Mack shortly became a philanthropist and community booster. He donated the Ralph Gibson McGill Library to Westminster College, New Wilmington, Pennsylvania.
He bought local homes in disrepair, fixed them, and rented them out.
He also stocked some of his own 1,700 acres (69 km2) with deer and buffalo. J. South. Mack Community Park in Indiana, Pennsylvania, the central gathering place of the town, continues to operate with funds from the J. South. Mack Foundation. Although Mack was only 60 in 1940, his health gave way, and he died after a stroke on September 27.
Four colleges sent their choirs, and Bob Jones preached the funeral.