 Karalasingham was secretary BLPI's Ceylon branch (1945), served on the editorial board of "New Spark" (1947–48), member of the BLPI central committee (1947–48) and was a delegate at BLPI conferences (1944, 1947, 1948).He was a delegate at the Third World Congress of the Fourth International in 1951.He studied law in Britain between 1952 and 1958 and on returning to Ceylon became an advocate of the Supreme Court.