In June 2007 he became co-chairman of The Left (Die Linke) party, formed by a merger of the PDS and the much smaller Labour and Social Justice – The Electoral Alternative.

In order to get a free university education he emigrated to Communist GDR at the age of 18, and after facing initial doubts due to his heritage was allowed to join the Socialist Unity Party in 1963, but did not rise to leadership positions until shortly after the fall of communism and the resulting purge of hardliners from the party.

[1]: 63  Subsequent investigations revealed that Bisky was registered by the Stasi with the code names of Bienert between 1966 and 1970, and as Klaus Heine[2] from 1987.

When Bisky was promoted, the Main Directorate for Reconnaissance (German: Hauptverwaltung Aufklärung) of the Stasi issued a statement where Bisky was described as "a reliable comrade, who strictly follows orders and always is honest with the Ministry for State Security (Stasi)" ("ein zuverlässiger Genosse, der sich strikt an die gegebenen Anweisungen hält und gegenüber dem MfS stets ehrlich war").

His youngest son, Stephan Bisky, died in late 2008 while working towards his neuro-informatics doctorate at the University of Edinburgh.