His historically most memorable act was to sign a non-aggression and mutual assistance treaty with the Soviet leaders in Moscow in September 1939.
It followed a brutal ultimatum from the Soviet Foreign Minister, Vyacheslav Molotov on 24 September.
I tell you—the Soviet Union needs enlargement of her security guarantee system; for this purpose she needs an exit to the Baltic Sea … I ask you, do not compel us to use force against Estonia.”[1] The enforced in this manner treaty gave the Soviet army a right to set up military bases in Estonia, and it significantly reduced Estonia's independence until Estonia was formally incorporated into the Soviet Union between June and August 1940.
Selter left Estonia in November 1939, resigning both as Foreign Minister and as a member of Parliament.
After Germany occupied Estonia between 1941 and 1944, and after it was re-incorporated into the Soviet Union in 1944, he stayed in Switzerland as an exiled diplomat and politician.