The MST was formed in 1982 by the merger of two important (and previously rival) socialist groups, the maoist Partido Socialista Revolucionario/PSR (Revolutionary Socialist Party) and the Guevarist/Marxist-Leninist Movimiento Socialista Popular (People's Socialist Movement).
Among its supporters are Rafael Feliciano Hernández twice-elected leader of the Teachers' Federation of Puerto Rico, on an openly socialist platform; Victor Rodriguez, student leader and spokesman of the UJS in the University of Puerto Rico at Rio Piedras; Pedro Colon Almenas, former political prisoner.