When his father died in 1914 in World War I, the family (mother, grandparents and Otakar with 3 siblings) moved to town Německý Brod.

In 1930 he was arrested and imprisoned as a leader of a group of students that painted anti-war slogans (his anti-militarism can be traced back to loss of his father and to the influence of his mother and grandfather Kadleček) on a church in Německý Brod.

He spent long periods of the 1930s in hiding, as he was wanted by Czechoslovak police and courts for numerous crimes, mostly involving illegal distribution of communist press.

Since 1941 was a member of Czechoslovak Central National Committee in France (Československý ústřední národní výbor pro Francii), from 1943 military officer in the same organization.

Since 1943 he was one of four staff officers who coordinated military activities of international groups in non-occupied France that were incorporated into the French Forces of the Interior (FFI).

[2] During his stay in Paris, Hromádko fell in love with Věra Waldes, a daughter of wealthy Czech industrial family.

After the return, Hromádko joined the International and Organizational Departments of the Secretariat of the Central Committee of the Communist Party of Czechoslovakia (ÚV KSČ), where he utilized his management skills and experience in building conspiracy networks.

[4] Department of National Front was officially part of Information bureau (Informační oddělení – headed by Bedřich Geminder, with Hromádko as his deputy), but in reality it was managed directly by the General Secretary Rudolf Slánský.

Between October 1945 and the 1948 Czechoslovak coup d'état, he has written instructional articles on topics such as: how to build and manage local party organizations;[5] how to gain support on the countryside and among youth;[6] how to lead pre-election campaign[7] and how to understand planned agricultural reform.

In February 1951, Hromádko was arrested and tried in a secret constructed trial of army officers together with Antonín Svoboda and Bedřich Kopold.

This has brought him complications form the interrogation teams and prison supervisors who interpreted it as “bad behavior.“ As a result of destalinization in Czechoslovakia, Hromádko was released 30 April 1956 and later fully rehabilitated.