Blach was the grandson of Blach's founder Julius Blach. As president of the company he was active in Birmingham's civic life. He chaired the Downtown Improvement Association. He initiated a War Bond Breakfast program to spur sales of bonds in the early days of World War II. The success of that local campaign caused it to spread nationwide. The United States Treasury appointed Blach to head the national program through the rest of the war.
Blach was married (Alice Wilton) and had two children (Harold Jr and Alice). He died in 1959 at his home on Fairway Drive after a sudden illness. Rabbi Milton Grafman officiated at his funeral and he was buried at Elmwood Cemetery.