The Irish Rebellion of 1641 was an uprising in Ireland, initiated on 23 October 1641 by Catholic gentry and military officers. Their demands included an end to anti-Catholic discrimination, greater Irish self-governance, and return of confiscated Catholic lands. Planned as a swift coup d'état to gain control of the Protestant-dominated central government, instead it led to the 1641–1653 Irish Confederate Wars, part of the wider Wars of the Three Kingdoms.

Despite failing to seize Dublin Castle, rebels under Felim O'Neill quickly over-ran most of Ulster, centre of the most recent land confiscations. O'Neill then issued the Proclamation of Dungannon, a forgery claiming he had been authorised by Charles I of England to secure Ireland against his opponents in England and Scotland. Many Royalist Anglo-Irish Catholics responded by joining the uprising, and the rebellion spread throughout Ireland.

In November, rebels besieged Drogheda and defeated a government relief force at Julianstown. Especially in Ulster, thousands of Protestant settlers were expelled or massacred, and Catholics killed in retaliation. By April 1642, Royalist troops held Dublin, Cork, and large areas around them, with much of Ulster occupied by a Scottish Covenanter army and local Protestant militia. This left approximately two thirds of Ireland under rebel control.

In May 1642, Ireland's Catholic bishops met at Kilkenny, and declared the rebellion a just war. Along with members of the Catholic nobility, they created an alternative government known as Confederate Ireland. For the next ten years, the Confederacy fought a four-sided war against Irish Royalists, Scottish Covenanters and English Parliamentarians.

The roots of the 1641 rebellion derived from the colonisation that followed the Tudor conquest of Ireland, and the alienation of the Catholic gentry from the newly-Protestant English state in the decades following. Historian Aidan Clarke writes that religion "was merely one aspect of a larger problem posed by the Gaelic Irish, and its importance was easily obscured; but religious difference was central to the relationship between the government and the colonists". During the decades between the end of the Elizabethan wars in 1603 and the outbreak of rebellion in 1641, the political position of the wealthier landed Irish Catholics was increasingly threatened by the English government of Ireland. As a result, both the Gaelic Irish, and the Old English communities increasingly defined themselves as Irish and were viewed as such by the newcomers.

The pre-Elizabethan population of Ireland is usually divided into the native Irish and Old English, many of whom were descendants of medieval English and Anglo-Normans settlers. These groups were historically antagonistic, with English settled areas such as the Pale around Dublin, Wexford, and other walled towns being fortified against the rural Gaelic clans. By the 17th century, the cultural divide between these groups, especially at elite social levels, was narrowing; many of the Old English spoke Irish, patronised Irish poetry and music, and have been described as being "More Irish than the Irish themselves". Writing in 1614, one author claimed that previously the Old English "despised the mere Irish, accounting them a barbarous people, void of civility and religion and [each viewed] the other as a hereditary enemy" but cited intermarriage "in former ages rarely seen", education of the Gaelic Irish and "the late plantation of New English and Scottish [throughout] the Kingdom whom the natives repute a common enemy; but this last is the principal cause of their union". In addition, the native population became defined by their shared Catholicism, as opposed to the Protestantism of the new settlers.

The Tudor conquest of the late 16th and early 17th century led to the Plantations of Ireland, whereby Irish-owned land was confiscated and colonised with British settlers. The biggest was the Plantation of Ulster, which utilised estates confiscated from the northern lords who went into exile in 1607. Around 80% of these were distributed to English-speaking Protestants, with the remainder going to "deserving" native Irish lords and clans. By 1641, the economic impact of the plantations on the native Irish population was exacerbated because many who retained their estates had to sell them due to poor management and the debts they incurred. This erosion of their status and influence saw them prepared to join a rebellion, even if they risked losing more.

Many of the exiles, such as Eoghan Ruadh Ó Néill, served in the Catholic armies of France and Spain, particularly the Army of Flanders. They formed a small émigré Irish community, militantly hostile to the English-run Protestant state in Ireland, but restrained by the generally good relations England had with Spain and France after 1604. In Ireland itself, resentment caused by the plantations was one of the main causes for the outbreak and spread of the rebellion, combined with Poynings' Law, which required Irish legislation to be approved by the Privy Council of England. The Protestant-dominated administration took opportunities to confiscate more land from longstanding Catholic landowners. In the late 1630s Thomas Wentworth, the Lord Deputy of Ireland, proposed a new round of plantations designed to expand Protestant cultural and religious dominance. Delays in their implementation caused by Charles' struggles with his political opponents in England and Scotland meant that Catholics still owned over 60% of land in 1641.