After the failure of the Munich Putsch of November 1923 and the ban on the Nazi Party, Ernst was active in various other right-wing anti-democratic organizations.

As adjutant, Ernst helped the Berlin commander Wolf-Heinrich Graf von Helldorff in preparing and carrying out the antisemitic Kurfürstendamm riot of 12 September 1931.

[3] On the evening of the Jewish New Year celebrations, around 1000 SA men attacked Jews leaving the synagogue and passers-by on the Kurfürstendamm.

However, according to Ian Kershaw, the consensus of nearly all historians is that Marinus van der Lubbe did set the Reichstag on fire.

[11] SA Leader Ernst Röhm had repeatedly called for a "second revolution" that would introduce socialism into the Reich and banish the old Conservative forces of business and government.

Ernst was arrested and brutally beaten in Bremerhaven together with his wife and his friend Martin Kirschbaum as he was about to get aboard a navy cruiser in order to travel to Tenerife where he planned to spend his honeymoon.

He was then flown back to Berlin and taken to the barracks of the Leibstandarte Adolf Hitler, where he was shot by a firing squad in the early evening of 30 June.

According to the official death list drawn up for internal-administrative use by the Gestapo, he was one of fourteen people shot on the grounds of the Leibstandarte.