After the war, he went on tour around the world to condemn the Nazi cause and educate people about why it is important to protect human rights.

Under his command, UC-67 achieved a temporary closing of the French port of Marseille by sinking ships in the area, by torpedoes, and by the laying of mines.

When the war drew to a close, he decided to become a preacher, a story he later recounted in his book Vom U-Boot zur Kanzel (From U-boat to Pulpit).

He subsequently pursued his earlier idea of becoming a Lutheran pastor and studied Protestant theology at the Westphalian Wilhelm University in Münster from 1919 to 1923.

After serving as the superintendent of the Inner Mission in the old-Prussian ecclesiastical province of Westphalia, Niemöller in 1931 became pastor of the Jesus Christus Kirche (comprising a congregation together with St. Anne's Church) in Dahlem, an affluent suburb of Berlin.

[14]: 235  In his autobiography, From U-Boat to Pulpit published in the spring of 1933, he called the time of "the System" (a pejorative name for the Weimar Republic) the "years of darkness" and hailed Adolf Hitler for beginning a "national revival".

[15] In 1933, Niemöller founded the Pfarrernotbund, an organization of pastors to "combat rising discrimination against Christians of Jewish background".

[13] Author and Nobel Prize laureate Thomas Mann published Niemöller's sermons in the United States and praised his bravery.

[5][17] American sociologist Werner Cohn lived as a Jew in Nazi Germany, and he also reports on antisemitic statements by Niemöller.

"[19] In her book Twisted Cross, Doris L. Bergen says, "Martin Niemöller explained how he, a self-professed antisemite, had come to oppose plans to exclude non-Aryans from the clergy.

Even his personal antipathy toward Jews, Niemöller indicated, had not blinded him to the realization that acceptance of an Aryan clause in the church would effectively negate the teaching of baptism.

"[20] In 1936, he signed the petition of a group of Protestant churchmen which sharply criticized Nazi policies and declared the Aryan Paragraph incompatible with the Christian virtue of charity.

However, he was immediately rearrested by Himmler's Gestapo – presumably because Rudolf Hess found the sentence too lenient and decided to take "merciless action" against him.

[21] While in the concentration camp, he "wrote to a military commander whom he had known in World War I asking to be released from Sachsenhausen so he could serve in the German Wehrmacht.

[23] His former cellmate, Leo Stein, was released from Sachsenhausen to go to America, and he wrote an article about Niemöller for The National Jewish Monthly in 1941.

I really believed, given the widespread anti-Semitism in Germany, at that time – that Jews should avoid aspiring to Government positions or seats in the Reichstag.

I am paying for that mistake now; and not me alone, but thousands of other persons like me.In late April 1945, Niemöller – together with about 140 high-ranking prisoners – was transported to the Alpenfestung.

[27] In 1959, he was asked about his former attitude toward Jews by Alfred Wiener, a Jewish researcher into racism and war crimes committed by the Nazi regime.

In a letter to Wiener, Niemöller stated that his eight-year imprisonment by the Nazis became the turning point in his life, after which he viewed things differently.

[10] He was soon a leading figure in the post-war German peace movement and was even brought to court in 1959 because he had spoken about the military in a very unflattering way.

[32][33] As a result, for the first time in human history, a World Constituent Assembly convened to draft and adopt a Constitution for the Federation of Earth.

He gave a sermon at the 30 April 1967 dedication of a Protestant "Church of Atonement" in the former Dachau concentration camp, which in 1965 had been partially restored as a memorial site.