Klaus Ernst (born 1 November 1954) is a German politician and was a leading member of the Labour and Social Justice Party, later The Left and switched to BSW in October 2023.

He is political economist has served as a member of The Left in the Bundestag since 2005, and as of 2010 had been co-chairing the party together with Gesine Lötzsch.

After his studies he became a trade union secretary in Stuttgart, responsible for organization, educational work and social plans.

Instead he pleaded for the establishment of a political alliance, an electoral alternative with regard to the German federal election in 2005.

[1] After being kicked out of the SPD he would join the Wahlalternative Arbeit und Soziale Gerechtigkeit (WASD) which would merge with the Party For Democratic Socialism to form Die Linke in June 2007.