The Irish Rebellion of 1641 (Irish: ir Amach 1641) was an uprising by Irish Catholics in the Kingdom of Ireland, who wanted an end to anti-Catholic discrimination, greater Irish self-governance, and to partially or fully reverse the plantations of Ireland. They also wanted to prevent a possible invasion or takeover by anti-Catholic English Parliamentarians and Scottish Covenanters, who were defying the king, Charles I. It began as an attempted coup d'tat by Catholic gentry and military officers, who tried to seize control of the English administration in Ireland. However, it developed into a widespread rebellion and ethnic conflict with English and Scottish Protestant settlers, leading to Scottish military intervention. The rebels eventually founded the Irish Catholic Confederacy.

Led by Felim O'Neill, the rebellion began on 23 October and although they failed to seize Dublin Castle, within days the rebels occupied most of the northern province of Ulster. O'Neill issued the Proclamation of Dungannon which claimed he had support from Charles to secure Ireland against his opponents. Although the document was a forgery, it encouraged many Anglo-Irish Catholics to join the uprising and soon most of Ireland was in rebellion. In November, rebels besieged Drogheda and defeated an English relief force at Julianstown. In its initial stages, especially in Ulster, the rebellion led to the death or eviction of thousands of Protestant settlers who responded in kind. Events such as the Portadown massacre outraged public opinion in England and Scotland and had a lasting impact on the Ulster Protestant community.

While both Charles and Parliament sought to quell the rebellion, neither side trusted the other with control of any army raised to do so, one of the issues that led to the First English Civil War in August 1642. The first English troops arrived in Dublin in December and recaptured much of the Pale and the area around Cork. In March 1642, Charles approved the Adventurers' Act, under which Parliament raised loans to fund further military intervention which would be repaid by confiscating rebel lands. In April, a Covenanter army landed in Ulster to protect their Presbyterian co-religionists and swiftly captured most of the eastern area of the province, while a local Protestant militia known as the Laggan Army held the northwest. Most of the rest of Ireland was under rebel control.

In May 1642, Ireland's Catholic bishops met at Kilkenny, declared the rebellion to be a just war and took steps to control it. With representatives of the Catholic nobility in attendance, they agreed to set up an alternative government known as the Irish Catholic Confederacy and drew up the Confederate Oath of Association. The rebels, now known as Confederates, held most of Ireland against the Protestant Royalists, Scottish Covenanters and English Parliamentarians. The rebellion was thus the first stage of the Irish Confederate Wars and part of the wider Wars of the Three Kingdoms, which would last for the next ten years.

Sir Phelim Roe O'Neill of Kinard (Irish: Féilim Rua Ó Néill na Ceann Ard; 1604–1653) was an Irish politician and soldier who started the Irish rebellion in Ulster on 23 October 1641. He joined the Irish Catholic Confederation in 1642 and fought in the Wars of the Three Kingdoms under his cousin, Owen Roe O'Neill, in the Confederate Ulster Army. After the Cromwellian conquest of Ireland O’Neill went into hiding but was captured, tried and executed in 1653.