After graduating in economics from Bocconi University, he became consultant for the Italian Minister of Finance in Romano Prodi's government.

In November 2009, Fassina started his political career as coordinator on economic issues for the Democratic Party.

On 2 May 2013, Fassina became the Italian Deputy Minister of Economy and Finances in the Enrico Letta government; he was dismissed on 4 January 2014,[1][2] in disagreement with the new party leader Matteo Renzi's political line.

[3] In May 2015, Fassina refused to support Renzi, who had become Prime Minister of Italy, and his proposal for a new Italian electoral law.

[8] In September 2018, Fassina founded Fatherland and Constitution, a left-wing souverainist political association.