He worked in the National Executive of the SPD and was the editor of the municipal policy magazine Die Gemeinde (The Community).

Fechner participated in the social-democratic resistance group led by Franz Künstler, and was jailed in 1933–1934 and 1944–1945 by the Nazi regime.

In 1948, Fechner succeeded Eugen Schiffer as President of the German Central Administration of Justice, he served from 1949 to 1951 as President of the Association of Democratic Lawyers, and was from October 1949 to July 1953 Minister of Justice of the newly created GDR.

Consequently, he was denounced as an "enemy of the state and the party", lost his ministerial charge, was expelled from the SED and arrested.

After a two-year-long detention without charge in the Stasi headquarters at Hohenschönhausen, he was sentenced to eight years of prison by the Supreme Court.