From 1918 to 1934, Estonia used a parliamentary political system, where the presidency and ministry were subject to parliamentary confidence, but instead of a presidential office, the government was headed by a prime minister and from 1920 to 1934, a similar office called State Elder (Riigivanem).
The 1934 constitution gave the State Elder the role of the president, with a separate head of government created, restoring the office of prime minister.
The new system was obstructed by a 1934 coup d'état by head of government Konstantin Päts.
Acting prime minister Otto Tief was in office for 8 days between the German and Soviet occupations in 1944.
Jaan Tõnisson was in office four times, although there was just one full day of Ado Birk's cabinet between his first two terms.
Longest interwar average term is held by Konstantin Päts (594 days).