In 1918 he became a functionary of the reborn Polish state, first as a commissar for the Łódź region in 1918, then from 1919 to 1920 as a starost of the Środa County and from 1923 to 1928 he was the voivode of Poznań.
In July 1940 he was chosen to be the Government Delegate for Poland for the Polish territories annexed by Nazi Germany although he did not receive the official nomination from general Władysław Sikorski until December 3.
Bniński was arrested by then Germans in July 1941, for refusing to express support for a joint Polish-German anti-Soviet declaration.
The exact circumstances of the disposal of his body are unknown; according to Zbigniew Mieczkowski he could have even been fed to wild animals (lions).
[2] It was not until 10 October 1942 that Nazi Germany's Foreign Ministry retroactively issued a death penalty for Bniński.