Partido Lakas ng Masa held its founding congress last January 30, 2009. The Congress was attended by more than 1,000 leaders representing various sectors, national organizations and formations in the country. The constitution and by-laws of the party was adopted in the Congress. Likewise, its first Party Chairperson and Party Council were elected during the founding Congress.

In November 30, 2009, with 5,000 activists, Partido Lakas ng Masa was publicly launched during the commemoration of Bonifacio Day. Its tri-color flag, which was used by General Gregorio del Pilar during the revolution against Spain and against the entry of US colonialist forces, dotted the streets and the “Pagbabago! Sosyalismo!” slogan reverberated though out the marching route in Manila during that day.

Around 10,000 workers and urban poor marched on May Day under the banner of Partido Lakas ng Masa and its allied mass organizations Bukluran ng Manggagawang Pilipino, Kongreso sa Pagkakaisa ng Maralitang Lungsod, Pagkakaisa ng Manggagawa sa Transportasyon, Aniban ng Manggagawa sa Agrikultura, Makabayan Pilipinas, Sanlakas, Kalayaan, Metro Manila Vendors Association and Samahang Demokratikong Kabataan. The slogans "Stop Retrenchments! Decent Work for All!" and "Capitalism is a Pestilence! Socialism for Change!" echoed throughout the streets of Manila.