He was elected to the Chamber of Deputies (Romania) in 1990, 1992 and 1996, and was a member of the Joint Romania-European Union Parliamentary Committee, and later of the Chamber's External Policies and European Integration Committee - under the PSDR-backed Romanian Democratic Convention (CDR) governments.
He retreated from public life after the subsequent union of the PSDR with the Romanian Party of Social Democracy (PDSR), which he had voted against.
His resignation came shortly after merging by absorption of PSDR by PDSR, the former FSN, which became the Social Democratic Party (PSD).
Sergiu Cunescu was a supporter of modern social democracy, of the Franco-German origin, mastering Bad Godesberg’s reformist theses, who delineated the European left-wing movement of Marxism.
Among his most important comrades were Radu Dimitrescu, Constantin Avramescu (until 1997), Smaranda Dobrescu, etc.