Holbrock was born in Hamilton, Ohio, the son of George H. and Clara C. (Beck) Holbrock. His father was a shoemaker by trade who became a successful merchant and partner with his younger brother William G. Holbrock in the Holbrock Brothers Dry Goods store in Hamilton and a branch, Middletown Dry Goods, in Middletown, Ohio.
He supported $7 billion in aid to Britain, Lend-Lease, and the 1941 amendment to the Neutrality Act to remove restrictions that forbade U.S. vessels from entering combat zones and US citizens from sailing on vessels of belligerents. In 1942, although favored to retain his seat, he was defeated for re-election.
After the war, Holbrock returned to the private practice of law, but remained very active in Democratic politics and was a delegate to the Democratic National Conventions in 1948 and 1960. He became chairman of the Butler County Democratic Executive Committee in 1950 and served sixteen years in that capacity until 1966.
Death
Greg John Holbrock died in 1992, aged 86, in Hamilton, Ohio. He was interred there with his wife Bernice in St. Stephen's Mausoleum.
