He worked as a history teacher in Osijek, Zemun, Petrinja and Zagreb secondary schools before and during the World War I.

During the war, Horvat was accused of being sympathetic to the Kingdom of Serbia and briefly detained in Hungary in response.

He published daily articles in the Jutarnji list [hr] paper in 1932–1940 and established the Hrvatski rodoljub (lit.

After the defeat of the Axis powers, Horvat was indicted for the positions he expressed in his article Ljetopis Hrvatske 1918. do 1942.

Annals of Croatia 1918–1942), convicted and sentenced to ten years of loss of political and civil rights.