 In 2003, with the election of Riccardo Illy as President of Friuli-Venezia Giulia, Cosolini is appointed Regional Councilor for Labor, Education, Universities and Research.After winning the centre-left primaries for the candidacy for the office of mayor of Trieste, Cosolini is elected mayor on May 2011.In 2016, Cosolini tries to achieve the reconfirmation, but he is defeated by his predecessor and centre-right candidate Roberto Dipiazza.