1883 appears to mark the first appearance of this slogan in print—in a pamphlet produced by the Democratic Federation. William Morris was the treasurer of the organization and included it on the cover of a book of songs published two years later.
Fellow-Citizens, we appeal to every man and woman among you who is weary of this miserable huckster’s society, where poverty and prostitution, fraud and adulteration, swindling and jobbery, luxury and debauchery reign supreme, we appeal to you to work with its in a never-ceasing effort to secure a happier lot for our people and their children, and to hold up a high ideal of national greatness for those who come after. Such an ideal of true greatness and glory, needs but intelligence, enthusiasm, and combination, to make it a reality even in our own day. We, at least, will never falter. We stretch out our hands for help, co-operation, and encouragement, to all creeds and all nationalities, ready ourselves to render assistance in every struggle against class injustice and individual greed. The land of England is no mean heritage ; there is enough and to spare for all; with the powers mankind now possess wealth may easily be made as plentiful as water at the expense of trifling toil. But to-day the worn-out wage-slaves of our boasted civilisation look hopelessly at the wealth which they have created to be devoured only by the rich and their hangers-on. To the abject poor patriotism is but a mockery, all talk of happiness, of beauty, of morality, is a sneer. We call, then, upon every lover of freedom to support us in our endeavour to form a real party of the people, which shall secure a noble future for our own and other lands.
The aims and objects of the DEMOCRATIC FEDERATION are before you. Success can only be achieved by organised effort.
Educate. We shall need all our intelligence.
Agitate. We shall need all our enthusiasm.
Organise. We shall need all our force.
EDUCATE! AGITATE! ORGANISE!
—Socialism Made Plain, the Social and Political Manifesto of the Democratic Federation (1883) (source)