After about 1220 he began to carry out missions for the Friars to Germany, and was put in charge of administering several convents, or religious communities, in that region and became vicar in the government of the German province. Around 1223, Thomas returned to Italy and lived near to Francis.
After Francis was canonized as a saint by the Church in 1228, Thomas was commissioned to write the first life of the saint by Pope Gregory IX. In 1247, he completed a second life of St. Francis, commissioned by the minister of the Franciscan order. He continued to write about St. Francis and his miracles, and to compose other writings in honor of St. Francis.
He also wrote a “Life of St. Clare of Assisi,” an ascetic early follower of St. Francis who, with her sister Agnes and other women, insisted on following a life of extreme poverty. Thomas of Celano’s works have been collected and remain in use in the order today. Thomas of Celano died about 1255.
Source: Kevin Knight, “Thomas of Celano,” Catholic Encyclopedia, New Advent, 2012, http://www.newadvent.org/cathen/14694a.htm.