Organised by a seven-man Military Council of the Irish Republican Brotherhood, the Rising began on Easter Monday, 24 April 1916, and lasted for six days. Members of the Irish Volunteers—led by schoolmaster and Irish language activist Patrick Pearse, joined by the smaller Irish Citizen Army of James Connolly and 200 women of Cumann na mBan—seized key locations in Dublin and proclaimed an Irish Republic. The British Army brought in thousands of reinforcements as well as artillery and a gunboat. There was fierce street fighting on the routes into the city centre, where the rebels put up stiff resistance, slowing the British advance and inflicting heavy casualties. Elsewhere in Dublin, the fighting mainly consisted of sniping and long-range gun battles. The main rebel positions were gradually surrounded and bombarded with artillery. There were isolated actions in other parts of Ireland, with attacks on the Royal Irish Constabulary barracks at Ashbourne, County Meath, County Cork and in County Galway, and the seizure of the town of Enniscorthy, County Wexford. Germany had sent a shipment of arms to the rebels, but the British had intercepted it just before the Rising began. Volunteer leader Eoin MacNeill had then issued a countermand in a bid to halt the Rising, which greatly reduced the number of rebels who mobilised.
With much greater numbers and heavier weapons, the British Army suppressed the Rising. Pearse agreed to an unconditional surrender on Saturday 29 April, although sporadic fighting continued until Sunday, when word reached the other rebel positions. After the surrender the country remained under martial law. About 3,500 people were taken prisoner by the British, many of whom had played no part in the Rising, and 1,800 of them were sent to internment camps or prisons in Britain. Most of the leaders of the Rising were executed following courts-martial. The Rising brought physical force republicanism back to the forefront of Irish politics, which for nearly 50 years had been dominated by constitutional nationalism. It, and the British reaction to it, led to increased popular support for Irish independence. In December 1918, republicans, represented by the reconstituted Sinn Féin party, won 73 seats in a landslide victory in the general election to the British Parliament. They did not take their seats, but instead convened the First Dáil and declared the independence of the Irish Republic. The Soloheadbeg ambush started the War of Independence.
485 people were killed in the Easter Rising. About 54% were civilians, 30% were British military and police, and 16% were Irish rebels. More than 2,600 were wounded. Many of the civilians were killed as a result of the British using artillery and heavy machine guns, or mistaking civilians for rebels. Others were caught in the crossfire in a crowded city. The shelling and the fires it caused left parts of inner city Dublin in ruins.
The Third Home Rule Bill was introduced by British Prime Minister H. H. Asquith in 1912. Unionists, who were Protestant, opposed it, as they did not want to be ruled by a Catholic-dominated Irish government. Led by Sir Edward Carson and James Craig, they formed the Ulster Volunteers (UVF) in January 1913. In response, Irish nationalists formed a rival paramilitary group, the Irish Volunteers, in November 1913. The Irish Republican Brotherhood (IRB) was a driving force behind the Irish Volunteers and attempted to control it. Its leader was Eoin MacNeill, who was not an IRB member. The Irish Volunteers' stated goal was "to secure and to maintain the rights and liberties common to all the people of Ireland". It included people with a range of political views, and was open to "all able-bodied Irishmen without distinction of creed, politics or social group". Another militant group, the Irish Citizen Army, was formed by trade unionists as a result of the Dublin Lock-out of that year. When the Irish Volunteers smuggled rifles into Dublin, the British Army attempted to stop them and fired into a crowd of civilians. British Army officers then threatened to resign if they were ordered to take action against the UVF. By 1914, Ireland seemed to be on the brink of a civil war. The crisis was ended in August that year by the outbreak of World War I and Ireland's involvement in it. The Home Rule Bill was enacted, but its implementation was postponed by a suspensory act until the end of the war.