A member of the Social Democratic Party of Austria, he served as mayor and governor of Vienna from 7 November 1994 until 24 May 2018.

Häupl has won three elections since his appointment as mayor; each of them has led to increased majorities for the SPÖ.

In the 1996 City Council election, the SPÖ lost its overall control of the 100-seat chamber with 43 seats on 39.15% of the vote.

On 14 December 2004 Häupl was elected unopposed to succeed Valéry Giscard d'Estaing as President of the Council of European Municipalities and Regions.

Häupl was awarded the Czech Order of the White Lion in October 2017 along with Gerhard Schröder and Borut Pahor.