He was born and raised an unbeliever, but came to faith in Christ as a young man. Not long after being baptised, he heard of Pachomius (May 15) and fled to join him in the desert. Saint Pachomius accepted Theodore as a monk and, because of his humility and obedience, came to esteem him most highly of all the brethren. Theodore’s sister joined him in the desert, taking up life in a women’s monastery and becoming its abbess. When their mother came to bring them back from the desert, she in turn was persuaded to stay in the women’s monastery as a monastic. Finally, Theodore’s brother Paphnutius also came to the monastery and was tonsured.
Once the Bishop of Panopolis asked Saint Pachomius to build a monastery for him; Pachomius entrusted Theodore to carry out the work. Some of the brethren grumbled at the authority given to Theodore, for he was younger than many of them; but St Pachomius said: ‘Theodore and I fulfill the same service for God; and he also has the authority to give orders as father.’ When St Pachomius reposed, he left St Theodore to be spiritual father to the monasteries that he had founded, a task which he faithfully fulfilled until his death at a great age.