[1] The son of a bricklayer, Gregor was born in Staré Město, Moravia.

After matriculation from the gymnasium, he began studies at the Faculty of Law of Masaryk University in Brno, where he graduated with a doctorate in 1935.

After completing his studies, Gregor was employed at the district courts in Uherské Hradiště and Brno, first as an auditor and from 1939 as a judge.

[2] After the occupation of the Czech lands by Nazi Germany in 1939, Gregor joined the anti-Nazi resistance movement in southern Moravia.

In January 1948, he was elected a member of the Central Committee of the KSČ, and in February, he was appointed Minister of Foreign Trade.