A former member of the historical Italian Socialist Party (PSI), Boselli was first elected as MP in 1994.

[1] From September 1999 to 2001, Boselli served as rapporteur for the second reading of the InfoSoc directive, having been named by the Committee on Legal Affairs and the Internal Market.

[2] Boselli was one of the main minds behind his party's decision to join forces with the Italian Radicals of Emma Bonino to found the Rose in the Fist, on the occasion of the 2006 Italian general election.

In 2007, he founded the new Socialist Party, with whom he participated in the 2008 Italian general election but obtained only 0.9% of the vote.

In December 2010, Boselli joined the centrist party Alliance for Italy, and became vice-president not long after.