They originated in the International Socialists from which they departed in 1974 to form a new group. In 1975 they joined with Workers Fight to form the International-Communist League which split into its constuent parts soon after. In 1980 Workers Power abandoned their position that the 'socialist states' were state capitalist and adopted the idea that they were deformed workers states. They have since changed this position twice.
Always linked with the tiny Irish Workers Group they have placed a great deal of emphasis on building an international organisation. Therefore they founded the Movement for a Revolutionary Communist International with the IWG, Group Arbeitermacht in Germany and Pouvoir Ouvrier in France. This added supporters in Austria, Peru and Bolivia and became the League for a Revolutionary Communist International. They then added a group in New Zealand.
Having grown they split and lost most of their supporters in New Zealand, all those in Peru and Bolivia and a few in Europe who formed the LCMRCI. More recently they have lost members in Austria and Paris. This has meant that they have disbanded their French group although rebranding as the League for the Fifth International.
The League for the Fifth International founded a youth organisation, known as Revolution, which is very closely linked with Workers' Power in the UK.