He served as the leader of a new Greek left-wing political party, Popular Unity, from 21 August 2015 until his resignation on 2 June 2019.

[1] Previously he was a member of Syriza, and from 27 January to 17 July 2015 he served in the cabinet of Alexis Tsipras as the Minister of Productive Reconstruction, Environment and Energy.

After the 2015 legislative election, he was appointed Minister of Productive Reconstruction, Environment and Energy in the cabinet of Alexis Tsipras on 27 January.

[3] He has called "for SYRIZA to [be] swept by a new wave of radicalization in all areas, ideological, political, programmatic", opposing "the Troika, memoranda, neoliberalism and finally capitalism itself",[4] and has spoken against continued Greek membership of the euro, describing the European Union as "totalitarian".

In a cabinet reshuffle on 17 July 2015, Lafazanis was removed from his role as the Minister of Productive Reconstruction, Environment and Energy.