The first indication of change came with the arrival of James Connolly in 1896. He had been invited by the Dublin Socialist Society as paid organiser, but by 1903 had left for the United States, frustrated by his lack of progress. Five years later, James Larkin took up the challenge. In 1906 he had been elected general organiser of the British-based National Union of Dock Labourers and it sent him to Dublin to recruit dock labour there in 1908. That year after a breach with his employers, he established his own union the Irish Transport and General Workers’ Union (ITGWU). Its purpose was to mobilise the city’s unskilled labour. By 1913 it had 10,000 members; it had rapidly become Ireland’s biggest and most militant union, with its own distinct blend of trade unionism, republicanism and socialism – ‘Larkinism’. Larkin himself was hero-worshipped by the Dublin working class.

In 1913, when labour problems were convulsing Britain and Larkin was at the height of his power, he determined to break the anti-union stance of the Dublin United Tramway Company (DUTC). It was owned by William Martin Murphy - a conservative nationalist and ex-MP, who was also proprietor of the city’s biggest newspaper, largest department store and hotel, and had founded the Dublin Employers’ Federation in 1912.

Ireland’s most bitter labour dispute began when Murphy demanded that all DUTC employees forswear membership of the ITGWU or be dismissed. Larkin immediately struck back by calling the tramway-men in his union out on 26 August 1913. The company responded by locking them out, at which point Larkin orchestrated a wave of ‘sympathetic strikes’, affecting other parts of Murphy’s empire as well as those businesses supporting him. After discussion, the employer’s federation then agreed to support the DUTC by locking out all employees who belonged to Larkin’s union and attempting to replace them with strike-breakers.

By late September, the dispute involved 20,000 employees across the city along with their 80,000 dependants. Violent clashes between workers and the police were frequent – especially at picket lines and where blackleg labour was being employed. The worst incident occurred on 31st August; Larkin was addressing a meeting in O’Connell Street, when the Dublin Metropolitan Police baton charged the crowd and arrested him. Prolonged rioting ensued during which two people were killed and 200 constables injured as well as numerous civilians.

By January 1914, it was evident that the workers had lost the dispute. Mostly unskilled and lacking the resources for a prolonged campaign, they had begun to drift back to work on the employers’ terms. By then the vital support they had received from British trade unions had reduced to a trickle and Larkin himself conceded, "We are beaten. We make no bones about it". But he had succeeded in mobilising the power of the Dublin labour force for the first time and employers thereafter dared not treat their employees with the same casual brutality and indifference as in the past. During the Rising, the tenement dwellers wreaked revenge on those businesses which had given Murphy support.

In October 1914 Larkin, worn out and frustrated, left Ireland for the United States. James Connolly ably filled the vacuum. Because of the dispute, he inherited a new weapon – the Irish Citizen Army, launched in November 1913. It had been formed to enable the locked out men to defend themselves in clashes with the police and to combat the demoralising impact of unemployment. Connolly stated that they should "drill and train as they were doing in Ulster". Its founding principle was that ‘the ownership of Ireland, moral and material, is vested by right in the people of Ireland’.