English Agitators
In the English-speaking world, the term first referred to men who were elected to present complaints of in army soldiers, including the New Model Army of Oliver Cromwell, during the English Civil War. They were also known as adjutators.

The practice begun in 1647 when the Long Parliament wanted to either disband the armies or sent them to Ireland. Soldiers did not appreciate that and eight of the cavalry regiments elected representatives they called commissioners, who presented the soldiers' complaints, including the fact that their payments were eight weeks late. In April 3, 1647 their letter was read in the House of Commons.

Other units followed suit and foot soldiers elected agitators who presented the declaration of the army. Officers supported them and co-signed their declaration. Cromwell and others promised payment.

Before the generals could return to London, parliament again decided to disband the army and settled June 1 as the date that would happen. Agitators resisted, soldiers of one regiment mutinied and refused to disband. In a conference on Thriplow Heath agitators demanded that the troops would march to London and "purge" the House of Commons.

Later Levellers adopted many of the Agitator's ideas.

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Negative sense
The term was first used in negative sense about those who supported Irish Home rule and eventual independence, especially Daniel O'Connell.