Becket was born about 1118, or in 1120 according to later tradition. He was born in Cheapside, London, on 21 December, which was the feast day of St Thomas the Apostle. He was the son of Gilbert Beket and Gilbert’s wife Matilda. Gilbert’s father was from Thierville in the lordship of Brionne in Normandy, and was either a small landowner or a petty knight. Matilda was also of Norman ancestry, and her family may have originated near Caen. Gilbert was perhaps related to Theobald of Bec, whose family also was from Thierville. Gilbert began his life as a merchant, perhaps as a textile merchant, but by the 1120s he was living in London and was a property owner, living on the rental income from his properties. He also served as the sheriff of the city at some point. They were buried in Old St Paul’s Cathedral.

One of Becket’s father’s wealthy friends, Richer de L’Aigle, often invited Thomas to his estates in Sussex where Becket was exposed to hunting and hawking. According to Grim, Becket learned much from Richer, who was later a signatory of the Constitutions of Clarendon against Thomas.  Beginning when he was 10, Becket was sent as a student to Merton Priory in England and later attended a grammar school in London, perhaps the one at St Paul’s Cathedral. He did not study any subjects beyond the trivium and quadrivium at these schools. Later, he spent about a year in Paris around age 20. He did not, however, study canon or civil law at this time and his Latin skill always remained somewhat rudimentary. Sometime after Becket began his schooling, Gilbert Beket suffered financial reverses, and the younger Becket was forced to earn a living as a clerk. Gilbert first secured a place for his son in the business of a relative – Osbert Huitdeniers – and then later Becket acquired a position in the household of Theobald of Bec, by now the Archbishop of Canterbury.

Theobald entrusted him with several important missions to Rome and also sent him to Bologna and Auxerre to study canon law. Theobald in 1154 named Becket Archdeacon of Canterbury, and other ecclesiastical offices included a number of benefices, prebends at Lincoln Cathedral and St Paul’s Cathedral, and the office of Provost of Beverley. His efficiency in those posts led to Theobald recommending him to King Henry II for the vacant post of Lord Chancellor, to which Becket was appointed in January 1155.  As Chancellor, Becket enforced the king’s traditional sources of revenue that were exacted from all landowners, including churches and bishoprics. King Henry even sent his son Henry to live in Becket’s household, it being the custom then for noble children to be fostered out to other noble houses. The younger Henry was reported to have said Becket showed him more fatherly love in a day than his father did for his entire life.

Becket was nominated as Archbishop of Canterbury in 1162, several months after the death of Theobald. His election was confirmed on 23 May 1162 by a royal council of bishops and noblemen. Henry may have hoped that Becket would continue to put the royal government first, rather than the church. The famous transformation of Becket into an ascetic occurred at this time.  Becket was ordained a priest on 2 June 1162 at Canterbury, and on 3 June 1162 was consecrated as archbishop by Henry of Blois, the Bishop of Winchester and the other suffragan bishops of Canterbury.  A rift grew between Henry and Becket as the new archbishop resigned his chancellorship and sought to recover and extend the rights of the archbishopric. This led to a series of conflicts with the king, including that over the jurisdiction of secular courts over English clergymen, which accelerated antipathy between Becket and the king. Attempts by King Henry to influence the other bishops against Becket began in Westminster in October 1163, where the King sought approval of the traditional rights of the royal government in regard to the church. This led to Clarendon, where Becket was officially asked to agree to the King’s rights or face political repercussions.

King Henry II presided over the assemblies of most of the higher English clergy at Clarendon Palace on 30 January 1164. In sixteen constitutions, he sought less clerical independence and a weaker connection with Rome. He employed all his skills to induce their consent and was apparently successful with all but Becket. Finally, even Becket expressed his willingness to agree to the substance of the Constitutions of Clarendon, but he still refused to formally sign the documents. Henry summoned Becket to appear before a great council at Northampton Castle on 8 October 1164, to answer allegations of contempt of royal authority and malfeasance in the Chancellor’s office. Convicted on the charges, Becket stormed out of the trial and fled to the Continent.  Henry pursued the fugitive archbishop with a series of edicts, aimed at all his friends and supporters as well as Becket himself; but King Louis VII of France offered Becket protection. He spent nearly two years in the Cistercian abbey of Pontigny, until Henry’s threats against the order obliged him to return to Sens. Becket fought back by threatening excommunication and interdict against the king and bishops and the kingdom, but Pope Alexander III, though sympathising with him in theory, favoured a more diplomatic approach. Papal legates were sent in 1167 with authority to act as arbitrators.  In 1170, Alexander sent delegates to impose a solution to the dispute. At that point, Henry offered a compromise that would allow Thomas to return to England from exile.

In June 1170, Roger de Pont L’Évêque, the archbishop of York, along with Gilbert Foliot, the bishop of London, and Josceline de Bohon, the bishop of Salisbury, crowned the heir apparent, Henry the Young King, at York. This was a breach of Canterbury’s privilege of coronation, and in November 1170 Becket excommunicated all three. While the three clergymen fled to the king in Normandy, Becket continued to excommunicate his opponents in the church, the news of which also reached Henry.  Upon hearing reports of Becket’s actions, Henry is said to have uttered words that were interpreted by his men as wishing Becket killed. The king’s exact words are in doubt and several versions have been reported. The most commonly quoted, as handed down by oral tradition, is “Will no one rid me of this turbulent priest?”, but according to historian Simon Schama this is incorrect: he accepts the account of the contemporary biographer Edward Grim, writing in Latin, who gives us “What miserable drones and traitors have I nourished and brought up in my household, who let their lord be treated with such shameful contempt by a low-born cleric?” Many variations have found their way into popular culture.  Whatever Henry said, it was interpreted as a royal command, and four knights, Reginald fitzUrse, Hugh de Morville, William de Tracy, and Richard le Breton, set out to confront the Archbishop of Canterbury.

On 29 December 1170 they arrived at Canterbury. According to accounts left by the monk Gervase of Canterbury and eyewitness Edward Grim, they placed their weapons under a tree outside the cathedral and hid their mail armour under cloaks before entering to challenge Becket. The knights informed Becket he was to go to Winchester to give an account of his actions, but Becket refused. It was not until Becket refused their demands to submit to the king’s will that they retrieved their weapons and rushed back inside for the killing. Becket, meanwhile, proceeded to the main hall for vespers. The four knights, wielding drawn swords, caught up with him in a spot near a door to the monastic cloister, the stairs into the crypt, and the stairs leading up into the quire of the cathedral, where the monks were chanting vespers.

Several contemporary accounts of what happened next exist; of particular note is that of Edward Grim, who was himself wounded in the attack. This is part of the account from Edward Grim:  …The wicked knight leapt suddenly upon him, cutting off the top of the crown which the unction of sacred chrism had dedicated to God. Next he received a second blow on the head, but still he stood firm and immovable. At the third blow he fell on his knees and elbows, offering himself a living sacrifice, and saying in a low voice, ‘For the name of Jesus and the protection of the Church, I am ready to embrace death.’ But the third knight inflicted a terrible wound as he lay prostrate. By this stroke, the crown of his head was separated from the head in such a way that the blood white with the brain, and the brain no less red from the blood, dyed the floor of the cathedral. The same clerk who had entered with the knights placed his foot on the neck of the holy priest and precious martyr, and, horrible to relate, scattered the brains and blood about the pavements, crying to the others, ‘Let us away, knights; this fellow will arise no more.