Wiechert was born in Kleinort near Sensburg , East Prussia.

He was one of the most widely read novelists in Germany during the 1930s. He incorporated his humanist ideals in his novels among which Das einfache Leben (The simple Life, 1939) and Die Jeromin-Kinder (The Jeromin children, 1945/47) are the best known today.

Wiechert was strongly opposed to Nazism from the start. He appealed in 1933 and 1935 to the undergraduates in Munich to retain their critical thinking in relation to the national socialist ideology. This was rated as call to internal resistance. The minutes of the speech circulated illegally in Germany and reached Moscow in 1937 baked in bread. Here it was published in the influential exile magazine Das Wort (The Word). But Wiechert went even further and dared to openly criticize the imprisonment of Martin Niemöller by the Nazis in 1938.

In consequence of his criticism, he was interned himself in the Buchenwald concentration camp for four months which became the most horrible time of his life. After that, he wrote down his memories about the time of his imprisonment and buried the manuscript. It was published after the war in 1945, entitled Der Totenwald (Forest of the dead), a shocking account of the conditions in Buchenwald. Joseph Goebbels had threatened after Wiechert's release from concentration camp that Wiechert would be killed if he publicly voiced protest once more.

After the war, Wiechert was a critic of restorative tendencies in post-war Germany. He died at Stäfa, Switzerland.