He was born into a Jewish family, his father was Sándor Schreiber and mother Lina Günsberger.

In 1906, the Association of Hungarian Private Officials was founded, for which he won the presidency.

On February 18, 1911, in Budapest, in Erzsébetváros, he married Mária (Krammer) Feldbránd , a civic school teacher, who was a daughter of Israel Feldbránd and Zsófia Treibitsch.

Szántó joined the Communist Party of Hungary at age 19, and was elected to the Central Committee in 1919.

In the Hungarian Soviet Republic, he served as People's Commissar for Defence.