After his studies were concluded he returned to England around 1141 where he gained the attention of Theobold, Archbishop of Canterbury, who sent him on several missions to Rome and ordained him a deacon in 1154. Soon after this, he was named Archdeacon of Canterbury. About this same time King Stephen died, leaving Henry the II as the new king. At Archbishop Theobold's urging, King Henry named Thomas the Lord High Chancellor of England. Thomas and King Henry were close friends and both spent a good deal of time “living it up.”
Thomas was so zealous in carrying out his duties as chancellor that many of the English clergy distrusted him. His loyalty to Henry, a Norman, was also seen by some as treachery since Thomas was a Saxon and should have been protecting the Saxons from the reaching of the Norman king.
When Archbishop Theobold died in 1161, King Henry thought that naming Thomas the new Archbishop of Canterbury would solidify his position as sole head of England; something that had long been opposed by Archbishop Theobold.
Thomas warned the King that if he were to become the Archbishop, he would fulfill his duty as zealously for the Church as he had as chancellor for England. The King insisted, even obtaining a dispensation from the Pope for Thomas to hold both positions. In 1162 Thomas was named Archbishop of Canterbury and immediately the conflicts that he had warned King Henry about began.
Read about the rest of his life here.