Born near Kyiv, Russian Empire,[1] Ominsky graduated from Southern High School in 1919.
In 1925, Ominsky received his bachelor's degree in economics from Wharton School of the University of Pennsylvania.
He practiced law in Philadelphia, Pennsylvania, and was involved with the Democratic Party.
From 1944 to 1946, Ominsky was a special attorney for the United States War Fraud Department.
In 1959 and 1960, Ominsky served as chief clerk of the Pennsylvania House of Representatives.