 Higgins instead joined the Trotskyist Socialist Labour League, soon leaving to join the Socialist Review Group which became the International Socialists (IS), and becoming the group's Secretary.By the 1960s, Higgins was a POEU branch secretary and was elected to the union's national executive, but he gave up his union work to become IS's full-time national secretary in the early 1970s.In a burst of internal quarrels in the period 1973-76 he left the organisation.