The second son of King James VI of Scotland and Anne of Denmark, Charles was born in Dunfermline Palace, Fife, on 19 November 1600. At a Protestant ceremony in the Chapel Royal at Holyrood Palace in Edinburgh on 23 December 1600, he was baptised by David Lindsay, Bishop of Ross, and created Duke of Albany, the traditional title of the second son of the King of Scotland, with the subsidiary titles of Marquess of Ormond, Earl of Ross and Lord Ardmannoch.

James VI was the first cousin twice removed of Queen Elizabeth I of England, and when she died childless in March 1603, he became King of England as James I. Charles was a weak and sickly infant, and while his parents and older siblings left for England in April and early June that year, due to his fragile health, he remained in Scotland with his father's friend Lord Fyvie, appointed as his guardian.

By 1604, when Charles was three-and-a-half, he was able to walk the length of the great hall at Dunfermline Palace without assistance, and it was decided that he was strong enough to make the journey to England to be reunited with his family. In mid-July 1604, Charles left Dunfermline for England where he was to spend most of the rest of his life. In England, Charles was placed under the charge of Elizabeth, Lady Carey, the wife of courtier Sir Robert Carey, who put him in boots made of Spanish leather and brass to help strengthen his weak ankles. His speech development was also slow, and he retained a stammer, or hesitant speech, for the rest of his life.

In January 1605, Charles was created Duke of York, as is customary in the case of the English sovereign's second son, and made a Knight of the Bath. Thomas Murray, a Presbyterian Scot, was appointed as a tutor. Charles learnt the usual subjects of classics, languages, mathematics and religion. In 1611, he was made a Knight of the Garter.

Eventually, Charles apparently conquered his physical infirmity, which might have been caused by rickets. He became an adept horseman and marksman, and took up fencing. Even so, his public profile remained low in contrast to that of his physically stronger and taller elder brother, Henry Frederick, Prince of Wales, whom Charles adored and attempted to emulate. However, in early November 1612, Henry died at the age of 18 of what is suspected to have been typhoid (or possibly porphyria). Charles, who turned 12 two weeks later, became heir apparent. As the eldest surviving son of the sovereign, Charles automatically gained several titles (including Duke of Cornwall and Duke of Rothesay). Four years later, in November 1616, he was created Prince of Wales and Earl of Chester.

In 1613, his sister Elizabeth married Frederick V, Elector Palatine, and moved to Heidelberg. In 1617, the Habsburg Archduke Ferdinand of Austria, a Catholic, was elected king of Bohemia. The following year, the Bohemians rebelled, defenestrating the Catholic governors. In August 1619, the Bohemian diet chose as their monarch Frederick V, who was leader of the Protestant Union, while Ferdinand was elected Holy Roman Emperor in the imperial election. Frederick's acceptance of the Bohemian crown in defiance of the Emperor marked the beginning of the turmoil that would develop into the Thirty Years' War. The conflict, originally confined to Bohemia, spiralled into a wider European war, which the English Parliament and public quickly grew to see as a polarised continental struggle between Catholics and Protestants. In 1620, Charles's brother-in-law, Frederick V, was defeated at the Battle of White Mountain near Prague and his hereditary lands in the Electoral Palatinate were invaded by a Habsburg force from the Spanish Netherlands. James, however, had been seeking marriage between the new Prince of Wales and Ferdinand's niece, Habsburg Princess Maria Anna of Spain, and began to see the Spanish match as a possible diplomatic means of achieving peace in Europe.

Unfortunately for James, negotiation with Spain proved generally unpopular, both with the public and with James's court. The English Parliament was actively hostile towards Spain and Catholicism, and thus, when called by James in 1621, the members hoped for an enforcement of recusancy laws, a naval campaign against Spain, and a Protestant marriage for the Prince of Wales. James's Lord Chancellor, Francis Bacon, was impeached before the House of Lords for corruption. The impeachment was the first since 1459 without the king's official sanction in the form of a bill of attainder. The incident set an important precedent as the process of impeachment would later be used against Charles and his supporters: the Duke of Buckingham, Archbishop Laud, and the Earl of Strafford. James insisted that the House of Commons be concerned exclusively with domestic affairs, while the members protested that they had the privilege of free speech within the Commons' walls, demanding war with Spain and a Protestant Princess of Wales. Charles, like his father, considered the discussion of his marriage in the Commons impertinent and an infringement of his father's royal prerogative. In January 1622, James dissolved Parliament, angry at what he perceived as the members' impudence and intransigence.

Partly inspired by his visit to the Spanish court in 1623, Charles became a passionate and knowledgeable art collector, amassing one of the finest art collections ever assembled. In Spain, he sat for a Sketch by Velázquez, and acquired works by Titian and Correggio, among others. In England, his commissions included the ceiling of the Banqueting House, Whitehall, by Rubens and paintings by other artists from the Low Countries such as van Honthorst, Mytens, and van Dyck. His close associates, including the Duke of Buckingham and the Earl of Arundel, shared his interest and have been dubbed the Whitehall Group. In 1627 and 1628, Charles purchased the entire collection of the Duke of Mantua, which included work by Titian, Correggio, Raphael, Caravaggio, del Sarto and Mantegna. His collection grew further to encompass Bernini, Bruegel, da Vinci, Holbein, Hollar, Tintoretto and Veronese, and self-portraits by both Dürer and Rembrandt. By Charles's death, there were an estimated 1760 paintings, most of which were sold and dispersed by Parliament.

Distrust of Charles's religious policies increased with his support of a controversial anti-Calvinist ecclesiastic, Richard Montagu, who was in disrepute among the Puritans. In his pamphlet A New Gag for an Old Goose (1624), a reply to the Catholic pamphlet A New Gag for the New Gospel, Montagu argued against Calvinist predestination, the doctrine that salvation and damnation were preordained by God. Anti-Calvinists – known as Arminians – believed that human beings could influence their own fate through the exercise of free will. Arminian divines had been one of the few sources of support for Charles's proposed Spanish marriage. With the support of King James, Montagu produced another pamphlet, entitled Appello Caesarem, in 1625 shortly after the old king's death and Charles's accession. To protect Montagu from the stricture of Puritan members of Parliament, Charles made the cleric one of his royal chaplains, increasing many Puritans' suspicions that Charles favoured Arminianism as a clandestine attempt to aid the resurgence of Catholicism.

With the failure of the Spanish match, Charles and Buckingham turned their attention to France. On 1 May 1625 Charles was married by proxy to the fifteen-year-old French Princess Henrietta Maria in front of the doors of the Notre Dame de Paris. Charles had seen Henrietta Maria in Paris while en route to Spain. The couple married in person on 13 June 1625 in Canterbury. Charles delayed the opening of his first Parliament until after the second ceremony, to forestall any opposition. Many members of the Commons were opposed to the king's marriage to a Roman Catholic, fearing that Charles would lift restrictions on Catholic recusants and undermine the official establishment of the reformed Church of England. Although he told Parliament that he would not relax religious restrictions, he promised to do exactly that in a secret marriage treaty with his brother-in-law Louis XIII of France. Moreover, the treaty loaned to the French seven English naval ships that would be used to suppress the Protestant Huguenots at La Rochelle in September 1625. Charles was crowned on 2 February 1626 at Westminster Abbey, but without his wife at his side because she refused to participate in a Protestant religious ceremony.

A large fiscal deficit had arisen in the reigns of Elizabeth I and James I. Notwithstanding Buckingham's shortlived campaigns against both Spain and France, there was little financial capacity for Charles to wage wars overseas. Throughout his reign Charles was obliged to rely primarily on volunteer forces for defence and on diplomatic efforts to support his sister, Elizabeth, and his foreign policy objective for the restoration of the Palatinate. England was still the least taxed country in Europe, with no official excise and no regular direct taxation. To raise revenue without reconvening Parliament, Charles resurrected an all-but-forgotten law called the "Distraint of Knighthood", in abeyance for over a century, which required any man who earned £40 or more from land each year to present himself at the king's coronation to be knighted. Relying on this old statute, Charles fined individuals who had failed to attend his coronation in 1626.

Charles provoked further unrest by trying to raise money for the war through a "forced loan": a tax levied without parliamentary consent. In November 1627, the test case in the King's Bench, the "Five Knights' Case", found that the king had a prerogative right to imprison without trial those who refused to pay the forced loan. Summoned again in March 1628, on 26 May Parliament adopted a Petition of Right, calling upon the king to acknowledge that he could not levy taxes without Parliament's consent, not impose martial law on civilians, not imprison them without due process, and not quarter troops in their homes. Charles assented to the petition on 7 June, but by the end of the month he had prorogued Parliament and re-asserted his right to collect customs duties without authorisation from Parliament.

On 23 August 1628, Buckingham was assassinated. Charles was deeply distressed. According to Edward Hyde, 1st Earl of Clarendon, he "threw himself upon his bed, lamenting with much passion and with abundance of tears". He remained grieving in his room for two days. In contrast, the public rejoiced at Buckingham's death, which accentuated the gulf between the court and the nation, and between the Crown and the Commons. Although the death of Buckingham effectively ended the war with Spain and eliminated his leadership as an issue, it did not end the conflicts between Charles and Parliament. It did, however, coincide with an improvement in Charles's relationship with his wife, and by November 1628 their old quarrels were at an end. Perhaps Charles's emotional ties were transferred from Buckingham to Henrietta Maria. She became pregnant for the first time, and the bond between them grew ever stronger. Together, they embodied an image of virtue and family life, and their court became a model of formality and morality.

In January 1629, Charles opened the second session of the English Parliament, which had been prorogued in June 1628, with a moderate speech on the tonnage and poundage issue. Members of the House of Commons began to voice opposition to Charles's policies in light of the case of John Rolle, a Member of Parliament whose goods had been confiscated for failing to pay tonnage and poundage. Many MPs viewed the imposition of the tax as a breach of the Petition of Right. When Charles ordered a parliamentary adjournment on 2 March, members held the Speaker, Sir John Finch, down in his chair so that the ending of the session could be delayed long enough for resolutions against Catholicism, Arminianism and tonnage and poundage to be read out and acclaimed by the chamber. The provocation was too much for Charles, who dissolved Parliament and had nine parliamentary Leaders, including Sir John Eliot, imprisoned over the matter, thereby turning the men into martyrs, and giving popular cause to their protest.

The king also derived money through the granting of monopolies, despite a statute forbidding such action, which, though inefficient, raised an estimated £100,000 a year in the late 1630s. One such monopoly was for soap, pejoratively referred to as "popish soap" because some of its backers were Catholics. Charles also raised funds from the Scottish nobility, at the price of considerable acrimony, by the Act of Revocation (1625), whereby all gifts of royal or church land made to the nobility since 1540 were revoked, with continued ownership being subject to an annual rent. In addition, the boundaries of the royal forests in England were restored to their ancient limits as part of a scheme to maximise income by exploiting the land and fining land users within the reasserted boundaries for encroachment. The focus of the programme was disafforestation and sale of forest lands for conversion to pasture and arable farming, or in the case of the Forest of Dean, development for the iron industry. Disafforestation frequently caused riots and disturbances including those known as the Western Rising.

By this stage Strafford, Lord Deputy of Ireland since 1632, had emerged as Charles's right-hand man and together with Laud, pursued a policy of "Thorough" that aimed to make central royal authority more efficient and effective at the expense of local or anti-government interests. Although originally a critic of the king, Strafford defected to royal Service in 1628 (due in part to Buckingham's persuasion), and had since emerged, alongside Laud, as the most influential of Charles's ministers.

When Charles attempted to impose his religious policies in Scotland he faced numerous difficulties. Although born in Scotland, Charles had become estranged from his northern kingdom; his first visit since early childhood was for his Scottish coronation in 1633. To the dismay of the Scots, who had removed many traditional rituals from their liturgical practice, Charles insisted that the coronation be conducted in the Anglican rite. In 1637, the king ordered the use of a new prayer book in Scotland that was almost identical to the English Book of Common Prayer, without consulting either the Scottish Parliament or the Kirk. Although it had been written, under Charles's direction, by Scottish bishops, many Scots resisted it, seeing the new prayer book as a vehicle for introducing Anglicanism to Scotland. On 23 July, riots erupted in Edinburgh upon the first Sunday of the prayer book's usage, and unrest spread throughout the Kirk. The public began to mobilise around a reaffirmation of the National Covenant, whose signatories pledged to uphold the reformed religion of Scotland and reject any innovations that were not authorised by Kirk and Parliament. When the General Assembly of the Church of Scotland met in November 1638, it condemned the new prayer book, abolished episcopal church government by bishops, and adopted Presbyterian government by elders and deacons.

The chief tax imposed by Charles was a feudal levy known as ship money, which proved even more unpopular, and lucrative, than poundage and tonnage before it. Previously, collection of ship money had been authorised only during wars, and only on coastal regions. Charles, however, argued that there was no legal bar to collecting the tax for defence during peacetime and throughout the whole of the kingdom. Ship money, paid directly to the Treasury of the Navy, provided between £150,000 to £200,000 annually between 1634 and 1638, after which yields declined. Opposition to ship money steadily grew, but the 12 Common law judges of England declared that the tax was within the king's prerogative, though some of them had reservations. The prosecution of John Hampden for non-payment in 1637–38 provided a platform for popular protest, and the judges found against Hampden only by the narrow margin of 7–5.

Charles perceived the unrest in Scotland as a rebellion against his authority, precipitating the First Bishops' War in 1639. Charles did not seek subsidies from the English Parliament to wage war, but instead raised an army without parliamentary aid and marched to Berwick-upon-Tweed, on the border of Scotland. Charles's army did not engage the Covenanters as the king feared the defeat of his forces, whom he believed to be significantly outnumbered by the Scots. In the Treaty of Berwick, Charles regained custody of his Scottish fortresses and secured the dissolution of the Covenanters' interim government, albeit at the decisive concession that both the Scottish Parliament and General Assembly of the Scottish Church were called.

The Long Parliament proved just as difficult for Charles as had the Short Parliament. It assembled on 3 November 1640 and quickly began proceedings to impeach the king's leading counsellors of high treason. Strafford was taken into custody on 10 November; Laud was impeached on 18 December; John Finch, now Lord Keeper of the Great Seal, was impeached the following day, and he consequently fled to the Hague with Charles's permission on 21 December. To prevent the king from dissolving it at will, Parliament passed the Triennial Act, which required Parliament to be summoned at least once every three years, and permitted the Lord Keeper and 12 peers to summon Parliament if the king failed to do so. The Act was coupled with a subsidy bill, and so to secure the latter, Charles grudgingly granted royal assent in February 1641.

In November 1641, the House of Commons passed the Grand Remonstrance, a long list of grievances against actions by Charles's ministers committed since the beginning of his reign (that were asserted to be part of a grand Catholic conspiracy of which the king was an unwitting member), but it was in many ways a step too far by Pym and passed by only 11 votes – 159 to 148. Furthermore, the Remonstrance had very little support in the House of Lords, which the Remonstrance attacked. The tension was heightened by news of the Irish rebellion, coupled with inaccurate rumours of Charles's complicity. Throughout November, a series of alarmist pamphlets published stories of atrocities in Ireland, which included massacres of New English settlers by the native Irish who could not be controlled by the Old English lords. Rumours of "papist" conspiracies circulated in England, and English anti-Catholic opinion was strengthened, damaging Charles's reputation and authority. The English Parliament distrusted Charles's motivations when he called for funds to put down the Irish rebellion; many members of the Commons suspected that forces raised by Charles might later be used against Parliament itself. Pym's Militia Bill was intended to wrest control of the army from the king, but it did not have the support of the Lords, let alone Charles. Instead, the Commons passed the bill as an ordinance, which they claimed did not require royal assent. The Militia Ordinance appears to have prompted more members of the Lords to support the king. In an attempt to strengthen his position, Charles generated great antipathy in London, which was already fast falling into lawlessness, when he placed the Tower of London under the command of Colonel Thomas Lunsford, an infamous, albeit efficient, career officer. When rumours reached Charles that Parliament intended to impeach his wife for supposedly conspiring with the Irish rebels, the king decided to take drastic action.

After a few skirmishes, the opposing forces met in earnest at Edgehill, on 23 October 1642. Charles's nephew Prince Rupert of the Rhine disagreed with the battle strategy of the royalist commander Lord Lindsey, and Charles sided with Rupert. Lindsey resigned, leaving Charles to assume overall command assisted by Lord Forth. Rupert's cavalry successfully charged through the parliamentary ranks, but instead of swiftly returning to the field, rode off to plunder the parliamentary baggage train. Lindsey, acting as a colonel, was wounded and bled to death without medical attention. The battle ended inconclusively as the daylight faded.

The war continued indecisively over the next couple of years, and Henrietta Maria returned to Britain for 17 months from February 1643. After Rupert captured Bristol in July 1643, Charles visited the port city and laid siege to Gloucester, further up the river Severn. His plan to undermine the city walls failed due to heavy rain, and on the approach of a parliamentary relief force, Charles lifted the siege and withdrew to Sudeley Castle. The parliamentary army turned back towards London, and Charles set off in pursuit. The two armies met at Newbury, Berkshire, on 20 September. Just as at Edgehill, the battle stalemated at nightfall, and the armies disengaged. In January 1644, Charles summoned a Parliament at Oxford, which was attended by about 40 peers and 118 members of the Commons; all told, the Oxford Parliament, which sat until March 1645, was supported by the majority of peers and about a third of the Commons. Charles became disillusioned by the assembly's ineffectiveness, calling it a "mongrel" in private letters to his wife.

In 1644, Charles remained in the southern half of England while Rupert rode north to relieve Newark and York, which were under threat from parliamentary and Scottish Covenanter armies. Charles was victorious at the battle of Cropredy Bridge in late June, but the royalists in the north were defeated at the battle of Marston Moor just a few days later. The king continued his campaign in the south, encircling and disarming the parliamentary army of the Earl of Essex. Returning northwards to his base at Oxford, he fought at Newbury for a second time before the winter closed in; the battle ended indecisively. Attempts to negotiate a settlement over the winter, while both sides re-armed and re-organised, were again unsuccessful.

At the battle of Naseby on 14 June 1645, Rupert's horsemen again mounted a successful charge against the flank of Parliament's New Model Army, but Charles's troops elsewhere on the field were pushed back by the opposing forces. Charles, attempting to rally his men, rode forward but as he did so, Lord Carnwath seized his bridle and pulled him back, fearing for the king's safety. Carnwath's action was misinterpreted by the royalist Soldiers as a signal to move back, leading to a collapse of their position. The military balance tipped decisively in favour of Parliament. There followed a series of defeats for the royalists, and then the Siege of Oxford, from which Charles escaped (disguised as a servant) in April 1646. He put himself into the hands of the Scottish Presbyterian army besieging Newark, and was taken northwards to Newcastle upon Tyne. After nine months of negotiations, the Scots finally arrived at an agreement with the English Parliament: in exchange for £100,000, and the promise of more money in the Future, the Scots withdrew from Newcastle and delivered Charles to the parliamentary commissioners in January 1647.

From Carisbrooke, Charles continued to try to bargain with the various parties. In direct contrast to his previous conflict with the Scottish Kirk, on 26 December 1647 he signed a secret treaty with the Scots. Under the agreement, called the "Engagement", the Scots undertook to invade England on Charles's behalf and restore him to the throne on condition that Presbyterianism be established in England for three years.

Charles's only recourse was to return to negotiations, which were held at Newport on the Isle of Wight. On 5 December 1648, Parliament voted by 129 to 83 to continue negotiating with the king, but Oliver Cromwell and the army opposed any further talks with someone they viewed as a bloody tyrant and were already taking action to consolidate their power. Hammond was replaced as Governor of the Isle of Wight on 27 November, and placed in the custody of the army the following day. In Pride's Purge on 6 and 7 December, the members of Parliament out of sympathy with the military were arrested or excluded by Colonel Thomas Pride, while others stayed away voluntarily. The remaining members formed the Rump Parliament. It was effectively a military coup.

The commission refused to allow Charles's burial at Westminster Abbey, so his body was conveyed to Windsor on the night of 7 February. He was buried in private in the Henry VIII vault alongside the coffins of Henry VIII and Henry's third wife, Jane Seymour, in St George's Chapel, Windsor Castle, on 9 February 1649. The king's son, Charles II, later planned for an elaborate royal mausoleum to be erected in Hyde Park, London, but it was never built.

With the monarchy overthrown, England became a republic or "Commonwealth". The House of Lords was abolished by the Rump Commons, and executive power was assumed by a Council of State. All significant military opposition in Britain and Ireland was extinguished by the forces of Oliver Cromwell in the Third English Civil War and the Cromwellian conquest of Ireland. Cromwell forcibly disbanded the Rump Parliament in 1653, thereby establishing the Protectorate with himself as Lord Protector. Upon his death in 1658, he was briefly succeeded by his ineffective son, Richard. Parliament was reinstated, and the monarchy was restored to Charles I's eldest son, Charles II, in 1660.

Ten days after Charles's execution, on the day of his interment, a memoir purporting to be written by the king appeared for sale. This book, the Eikon Basilike (Greek for the "Royal Portrait"), contained an apologia for royal policies, and it proved an effective piece of royalist propaganda. John Milton wrote a Parliamentary rejoinder, the Eikonoklastes ("The Iconoclast"), but the response made little headway against the pathos of the royalist book. Anglicans and royalists fashioned an image of martyrdom, and in the Convocations of Canterbury and York of 1660 King Charles the Martyr was added to the Church of England's liturgical calendar. High church Anglicans held special services on the anniversary of his death. Churches, such as those at Falmouth and Tunbridge Wells, and Anglican devotional societies such as the Society of King Charles the Martyr, were founded in his honour.

The executioner was masked and disguised, and there is debate over his identity. The commissioners approached Richard Brandon, the Common hangman of London, but he refused, at least at first, despite being offered £200. It is possible he relented and undertook the commission after being threatened with death, but there are others who have been named as potential candidates, including George Joyce, william Hulet and Hugh Peters. The clean strike, confirmed by an examination of the king's body at Windsor in 1813, suggests that the execution was carried out by an experienced headsman.

Parliament held Charles under house arrest at Holdenby House in Northamptonshire until Cornet George Joyce took him by threat of force from Holdenby on 3 June in the name of the New Model Army. By this time, mutual suspicion had developed between Parliament, which favoured army disbandment and Presbyterianism, and the New Model Army, which was primarily officered by Independent non-conformists who sought a greater political role. Charles was eager to exploit the widening divisions, and apparently viewed Joyce's actions as an opportunity rather than a threat. He was taken first to Newmarket, at his own suggestion, and then transferred to Oatlands and subsequently Hampton Court, while more ultimately fruitless negotiations took place. By November, he determined that it would be in his best interests to escape – perhaps to France, Southern England or to Berwick-upon-Tweed, near the Scottish border. He fled Hampton Court on 11 November, and from the shores of Southampton Water made contact with Colonel Robert Hammond, Parliamentary Governor of the Isle of Wight, whom he apparently believed to be sympathetic. Hammond, however, confined Charles in Carisbrooke Castle and informed Parliament that Charles was in his custody.