In June 2015 Stefano Fassina, a former deputy minister in the Letta Cabinet, left the Democratic Party over disagreements with Matteo Renzi, then PD leader and Prime Minister. In doing this he was followed by his long-time ally. In July, during a convention, Fassina launched Future to the Left, an incubator of a new left-leaning party, with other movements and breakaway groups such as Possible and Left Ecology Freedom. In November one senator and three more deputies left the party in protest against Renzi. D'Attorre, who holds a doctorate in philosophy from the Sant'Anna School of Advanced Studies, wrote a manifesto for a new "labour" party, which was signed also by the other five MPs and, which read: "The genetic mutation of the PD, born as central force of the Italian centre-left, is unfortunately already completed. The Renzi experience and the introduced mutations won't be a parenthesis. They have already altered in a irreversible way the perception of the PD and its function in the collective imagination". Subsequently, a parliamentary group under the banner of Italian Left was formed in the Chamber of Deputies, whose core was formed by SEL.
In February 2016 SI held its constituent assembly in Rome. Consequently, SI was established as a sub-group within the Mixed Group in the Senate: five senators of SEL, two dissidents from the Five Star Movement and one former Democrat joined, while two SEL senators refused to join and left their party altogether. Several lists named after SI participated in the 2016 local elections. The party did particularly well in Sesto Fiorentino, a medium-sized city in the metropolitan area of Florence, where it won 17.5% of the vote and its candidate for mayor was elected in the run-off with 65.5%, by beating his Democratic opponent. In December 2016 SEL was dissolved, in order to merge it into SI in early 2017.
Founding congress
In February 2017 SI was officially formed and Nicola Fratoianni was elected as its first secretary. Contextually, SI leader in the Chamber of Deputies Arturo Scotto, D'Attorre, Galli and Folino led a splinter group into the Article One – Democratic and Progressive Movement, a party formed by left-wing splinters of the PD. In March 2017 SI welcomed the four deputies of Possible in its group in the Chamber. In April Campanella left the party, leaving it with seven senators. On 24 June 2017 SI was accepted into the Party of the European Left as an observer member.
Free and Equal
On 3 December 2017 SI, together with the MDP and Possible, established Free and Equal, a left-wing joint list for the 2018 general election, and chose the President of the Senate and former anti-Mafia prosecutor Pietro Grasso as its leader and candidate for Prime Minister. In the election, SI obtained three deputies and one senator. In October SI, focused on forming an alliance with Luigi de Magistris' Popular Coalition for the 2019 European Parliament election, broke with the MDP and LeU. In January 2019, after the MDP's departure, SI returned into LeU's fold and, under the leadership of senator Francesco Laforgia and deputy Luca Pastorino, the two organisations initiated a collaboration with the goal of forming a joint party by March.
Composition
The party's founding members were: Along these, some youth organisations, local groups and individuals have joined SI.
