After a long leave due to political and institutional commitments, he returned to university teaching from 1994 to 1999.

He started his political career with the Italian Socialist Party, where he was elected to the municipal council of Venice.

The judge, on the second verdicts, gave unquestionably confirmed the right to use the symbol and the secretary to Gianni De Michelis.

In October 2007, De Michelis joined the newly formed Socialist Party, made up of the diaspora of the historical PSI.

At this time, De Michelis along with fellow former NPSI MEP Alessandro Battilocchio were admitted into the parliamentary group of the Party of European Socialists.