Opposition party formed as a result of a merger between three leftist parties; the United Left, the Progressives and Reformists and the Democratic Laboratory in 2017.
Party formed ahead of elections on December 8, 2019 a single list, called LIBERA (Free San Marino), with the Civic 10 political movement, MIS (Movimento Ideali Socialisti) and RES (Reforms and Development). LIBERA picked up 10 seats.
SDL is led by president Michele Muratori and party secretary Alessandro Bevitori [Sinistra Socialista Democratica (SSD)].
