The state parliament consisted of a landtag with a fluctuating number of members but not more than 48, elected for a term of three years by universal suffrage.

[1] For most of the Weimar period, due to the political stalemate in the landtag with neither the parties of the left nor the right able to form a stable parliamentary coalition, the state governments usually were headed by non-partisan technocrats.

[2] From 1925 to 1927, following Bavaria's lead, Oldenburg was one of many German states that issued a ban on Adolf Hitler's participation in public meetings.

The state originally consisted of the main district of Oldenburg Land, as well as the two exclaves of Eutin near the Baltic coast and Birkenfeld in southwestern Germany.

As a result of the Greater Hamburg Act it lost both exclave districts to Prussia and gained the City of Wilhelmshaven in return, effective 1 April 1937.