When Czechoslovakia was again established as a unified state, the KSS was still a separate party for a while (1945–1948).

After the merger KSS functioned as a regional affiliate of the KSČ, not as an independent political institution.

Therefore, the organizational structure of the KSS mirrored that of the KSČ: the KSS Congress held session for several days every five years (and just before the KSČ's Congress), selecting its Central Committee members and candidate members, who in turn selected a Presidium, a Secretariat, and a First Secretary (i.e. party leader).

KSS ceased to exist in 1990 (following the Velvet Revolution), when it was transformed into the independent social democratic party called the Party of Democratic Left (SDĽ).

Most of that party, in turn, is now part of Direction – Social Democracy, which had separated from the SDĽ in 2000.