Theodore was the third son of John I Doukas, ruler of Thessaly by his wife, who is only known by her monastic name Hypomone ("Patience").
[1][2] When John died in or shortly before 1289, he was succeeded by Theodore's older brother Constantine, but Theodore served as his co-ruler.
Initially, the two brothers were under the tutelage of Anna Palaiologina Kantakouzene as they were underage.
[3] Awarded the title of sebastokrator from the Byzantine emperor in 1295, he was scheduled to marry the Armenian princess Theophano, daughter of King Leo II, but this project fell through.
[2] He was defeated in battle by the Byzantine general Michael Doukas Glabas Tarchaneiotes, and died in c. 1299.