Born into a journalistic family, Hronek was the son of editor Isidor Langstein (1879–1942) and Růžena, née Picková (1881–1942).
His sister was murdered in Auschwitz,[2] his mother at Maly Trostenets,[3] and his father in the Izbica Ghetto.
Following the annexation of Austria to Nazi Germany in March 1938, he relocated to Paris as correspondent of the publishing house Melantrich.
After the occupation of France, he fled to London, where he worked at the Czechoslovak Ministry of Foreign Affairs from 1940 to 1945.
In 1946, Hronek was part of the Czechoslovak delegation to the founding Congress of the International Organization of Journalists (IOJ) in Copenhagen.