The party initially had more success in local than in national elections, and became especially strong in the north of England, particularly in Manchester and Bradford.  Although in 1900 the party joined with other groups such as the Social Democratic Federation, the Fabian Society and trade unions to form the Labour Representation Committee, which in 1906 became the Labour Party, the ILP maintained its independent position within the Labour movement.

The ILP took very much to heart the idea of international working class solidarity – 'brotherhood' was the word they used at the time – with the belief that wars were engineered out of capitalist profit-making greed, and that if only workers of all countries would refuse to fight, war would become impossible.  It is not surprising, therefore, that when war came in 1914, the Labour Leader, the paper of the ILP, became a focus of resistance.  The No-Conscription Fellowship, the main organisation to oppose conscription and then to support conscientious objectors, was founded following an appeal in its columns by its editor, Fenner Brockway.

With the imposition of conscription in 1916, ILP members were in the forefront of resistance, many becoming 'absolutists', refusing any form of conscription, and facing long years of imprisonment as mere 'political objectors', some being amongst those who were formally sentenced to death but reprieved.

Keir Hardie died in 1915, some thought of a broken heart, having failed to prevent the slaughter he had so valiantly striven against.   A new generation of ILP MPs, however, arose from the former imprisoned COs, including Fenner Brockway, Emrys Hughes and James Maxton.

Because of its radical propensities and its abiding social conscience on issues such as poverty, housing and education, the ILP had an uneasy relationship throughout its affiliation to the Labour Party.  In the 1980s it ceased to function as a political party, becoming a radical publishing house, Independent Labour Publications.