At the age of 15 he left his home and school because of his violent father. In 1970 he found work as an electronics technician and was elected youth representative and member of the works council. In 1972 he became a member of the German Metalworkers' Union and in 1974 he took the chair of regional trade unions youth organization in Munich (until 1979) and became a partymember of the Social Democratic Party of Germany. From 1979 to 1984 he studied political economy at the University of Hamburg.
After his studies he became a trade union secretary in Stuttgart, responsible for organization, educational work and social plans. In 1995 Ernst was elected plenipotentiary of the IG Metall in Schweinfurt.