Hard times descended upon Germany, and Anton felt that socialist revolutionaries had sabotaged the war effort and incited the people against the monarchy just to ride the dissension into power. In particular, Anton was infuriated by Kurt Eisner, a revolutionary in Bavaria. Eisner had been jailed for inciting labor strikes throughout the war but, upon release, had led Bavaria into revolution and become the new premier in Bavaria under the new government. Eisner served until 21 February 1919, when Anton shot Eisner dead on a Munich street. Anton made his motive clear:
"Eisner is a Bolshevist, a Jew; he isn't German, he doesn't feel German, he subverts all patriotic thoughts and feelings. He is a traitor to this land."
- Anton Graf von Arco auf Valley
In the aftermath of the attack, Anton became a hero who had stood up to the "traitors and saboteurs" that had seized power in Germany and earned the admiration of a young Joseph Goebbels, who happened to be in Munich at the time.
Hardline Bolshevik socialists and anarchists responded to the event with a murder spree throughout Munich, targeting the old elite. In April 1919, they overthrew the new government and established the Bavarian Soviet Republic. Nonetheless, the government was eventually re-taken by the socialist democrats, who had begun to align with Germany's reactionary and ultra-nationalist forces to crush the Bolshevik socialists and anarchists.
Under the restored government, Anton's trial began, in January 1920. The court sentenced Anton to death, but a conservative judge eventually reduced the sentence to five years in prison. The State Prosecutor said of Anton:
"If the whole German youth were imbued with such a glowing enthusiasm we could face the future with confidence."In 1925, after serving part of his sentence at Stadelheim prison in cell 70, Anton was released to make way for a new prisoner by the name of Adolf Hitler. Anton remained on probation until 1927. By that time, his name had disappeared from the political spotlight. Though he favored the establishment of a federalist government, Anton was remembered and decorated by the Nazi regime as a pro-German "hero of the movement".
In 1945, shortly after the Second World War ended, Anton was in a fatal car accident in Salzburg. He was survived by his mother, his wife, who passed in 1987, and four daughters.
