St. Thalelaeus was born in Lebanon (in Phoenicia) during the reign of the Eastern Emperor Numerius (AD 283-284). He was the son of Verukios (sometimes referred to as Berucius), a Bishop (or possibly an archpriest) of the church of Lebanon, and his wife, mother Romula. (His father is sometimes said to have been a Roman general.)
Thalelaeus exhibited at an early age the scientific curiosity and skill that convinced his father he would make an excellent physician, and he bacame edcutated as such, while retaining his zeal as a follower of Christ.
As was a common practice of professionals of that day, St. Thalelaeus established a clinic in his home at Anazarbus, Cilicia. No one was turned away, and only those who could afford it paid a fee for his services. On Sundays he went out to preach the word of Jesus Christ, always reminding his listeners that "of the most high cometh healing." His impassioned oratory brought many into the fold, the healthy as well as the sick. Soon he was looked upon with awe because he performed miraculous cures which could only be effected through Jesus.
St. Thalelaeus' works soon came to the attention of the Pagans who ruled Lebanon, and they sought to imprison or kill him. Nevertheless, he traveled throughout the country, carrying on the work of the Lord which he had accepted with great humility and dedication. In his travels he was exposed to the treachery of those who, through jealousy, envy, or simple evil, sought to oppose him and Our Lord. He went to Cilicia, and, when in Anazarbus, he was informed his enemies were near, he hid himself in an olive grove; but he was seized and taken to Aegae of Cilicia (mistakenly called Edessa, Syria, in the Roman Martyrology), and brought before Theodore, governor of the province of Cilicia, whose fiendish delight was to wreak all manner of destruction on the Christian Church and its champions.
Theodore prided himself as a debater, and challenged St. Thalelaeus, that they argue their opposing religions. The debate quickly turned into a defeat for the governor and his gods. Seeing the futility of his course, Theodore ordered the physician to be tortured. Through past experience the governor presumed that a punishment of the body would break the spirit and he would emerge victorious after all. When the tortures changed neither St. Thalelaeus' faith nor his ability to win at debate, the governor ordered him to be executed. When attempts to kill St. Thalelaeus by drowning failed, he was martyred by beheading, on May 20, 284 A.D.
St. Thalelaeus was exceeded in reputation as a combination of physician and missionary only by the Evangelist Saint Luke, through whom one of the Gospels was preserved in writing. He was as renouned as Hippocrates. He was able to cure the ills of his patients, not only with the medical skill he acquired in his profession but also with the miraculous help of Jesus Christ. His life story is unique among the saints because of the dual nature of his healing medically and miraculously through his dedication to the word of the Lord.
Also martyred with him were Alexander and Asterius, two bystanders, who may have been the officers in charge of his execution, because of their compassion for him, and other spectators who were converted by his constancy.
Exemplified in his lifetime the highest order of mankind in the image of God, and known as "the merciful", Saint Thalelaeus is one of the Holy Unmercenaries.