The Matara mayor has been appointed as organizer.
The central committee of the SLFP also sacked Sripathi Sooriyaarachchi from his post as organizer in Kelaniya but no replacement has been made yet, Sirisena said.
Samaraweera also holds the post of Treasurer of the SLFP.
The two were sacked from their ministerial positions earlier, have been carrying a campaign against President Mahinda Rajapakse and his two brothers who hold the posts of defence secretary and presidential advisor.
Last week Samaraweera and Suriarachchi lodged a complaint at Sri Lanka's bribery commission calling for an investigation into a purchase of fighter aircraft.
Bank accounts of a newspaper run by an ally of Samaraweera was also frozen and a director arrested under Sri Lanka's tough anti-terrorist laws.