Clad in a rough garment, barefoot, and, after the Evangelical precept, without staff or scrip, he began to preach repentance. He was soon joined by his first follower, a prominent fellow townsman, the jurist Bernardo di Quintavalle, who contributed all that he had to the work. Many other companions joined Francis, and reached the number of eleven within a year. Francis chose never to be ordained a priest, and the community lived as "fratres minores", in Latin, "lesser brothers". The Franciscans are sometimes called Friars Minor, a term derived from "fratres", in Latin, "brothers".

The brothers lived a simple life in the deserted lazar house of Rivo Torto near Assisi; but they spent much of their time wandering through the mountainous districts of Umbria, always cheerful and full of songs, yet making a deep impression on their hearers by their earnest exhortations.

In 1209 Francis led his first 11 followers to Rome to seek permission from Pope Innocent III to found a new religious order. At first his attempt to speak with the Pope was refused; but the following night, according to accounts, Innocent saw in a dream the church was crumbling apart and a poor man appearing to hold it up. The next morning, recalling the poor man he had refused the day before, he recognized him as the man he saw in his dream, and decided to change his verdict the following day

In 1215 Francis went again to Rome for the Fourth Lateran Council. During this time, he probably met Dominic de Guzman.

In 1216 Francis received from the new pope Honorius III the confirmation of the indulgence of the Porziuncola, now better known as the Pardon of Assisi : which the Pope decreed to be a complete remission of their sins for all those who prayed in the Porziuncola.

In 1217 the growing congregation of friars was divided in provinces and groups were sent to France, Germany, Hungary, Spain and to the East.

In 1219 Francis left, together with a few companions, on a pilgrimage of non-violence to Egypt. Crossing the lines between the sultan and the Crusaders in Damietta, he was received by the sultan Melek-el-Kamel.[2] Francis challenged the Muslim scholars to a test of true religion by fire; but they retreated. When Francis proposed to enter the fire first and, if he left the fire unharmed, the sultan would have to recognize Christ as the true God, the sultan was so impressed that he allowed him to preach to his subjects.[3] Though he didn't succeed in converting the sultan, the last words of the sultan to Francis of Assisi were, according to Jacques de Vitry, bishop of Acre, in his book "Historia occidentalis, De Ordine et praedicatione Fratrum Minorum (1221)" : “Pray for me that God may deign to reveal to me that law and faith which is most pleasing to him.”.

At Saint Jean d'Acre, the capital of what remained of the Kingdom of Jerusalem, he rejoined the brothers Elia and Pietro Cattini. Francis then most probably visited the holy places in Palestine in 1220.

Around 1220 St Francis of Assisi celebrated Christmas by setting up the first presepio or crèche (Nativity) in the town of Greccio near Assisi. He used real animals to create a living scene so that the worshipers could contemplate the birth of the child Jesus in a direct way, making use of the senses, especially sight.

When receiving a report of the martyrdom of five brothers in Morocco, he returned to Italy via Venice. Cardinal Ugolino di Conti was then nominated by the Pope as the protector of the order. When problems arose in the order, a detailed rule became necessary. On 29 September 1220 Francis handed over the governance of the order to brother Pietro Cattini at the Porziuncola. However, Brother Cattini died on 10 March 1221. He was buried in the Porziuncola. But when numerous miracles were attributed to the late Pietro Cattini, people started to flock to the Porziuncola, disturbing the daily life of the Franciscans. Francis then prayed, asking Pietro to stop the miracles and obey in death as he had obeyed him during his life. The report of miracles ceased. Brother Pietro was succeeded by brother Elia as vicar of Francis.

On 29 November 1223 the final rule of the order (in twelve chapters) was approved by Pope Honorius III.

While he was praying on the mountain of Verna, during a forty day fast in preparation for Michaelmas, Francis is said to have had a vision on or about 14 September 1224, the Feast of the Exaltation of the Cross, as a result of which he received the stigmata. Brother Leo, who had been with Francis at the time, left a clear and simple account of the event,[5] the first definite account of the phenomenon of stigmata. "Suddenly he saw a vision of a seraph, a six-winged angel on a cross. This angel gave him the gift of the five wounds of Christ."

Suffering from these Stigmata and from an eye disease, he had been receiving care

On 16 July 1228 he was pronounced a saint by the next pope Gregory IX, the former cardinal Ugolino di Conti, friend and protector of St. Francis. The next day, the pope laid the foundation stone for the Basilica of Saint Francis in Assisi.

St. Francis is considered the first Italian poet by literary critics. He believed commoners should be able to pray to God in their own language, and he wrote always in dialect of Umbria instead of Latin. His writings are considered to have great literary value, as well as religious.

"My sister birds, you owe much to God, and you must always and in everyplace give praise to Him; for He has given you freedom to wing through the sky and He has clothed you…you neither sow nor reap, and God feeds you and gives you rivers and fountains for your thirst, and mountains and valleys for shelter, and tall trees for your nests. And although you neither know how to spin or weave, God dresses you and your children, for the Creator loves you greatly and He blesses you abundantly. Therefore… always seek to praise God."

These legends exemplify the Franciscan mode of charity and poverty as well as the saint's love of the natural world. Part of his appreciation of the environment is expressed in his Canticle of the Sun, a poem written in Umbrian Italian in perhaps 1224 which expresses a love and appreciation of Brother Sun, Sister Moon, Mother Earth, Brother Fire, etc. and all of God's creations personified in their fundamental forms. In "Canticle of the Creatures," he wrote: "All praise to you, Oh Lord, for all these brother and sister creatures."[1]

Francis's attitude towards the natural world, while poetically expressed, was conventionally Christian. He believed that the world was created good and beautiful by God but suffers a need for redemption because of the primordial sin of man. He preached to man and beast the universal ability and duty of all creatures to praise God (a common theme in the Psalms) and the duty of men to protect and enjoy nature as both the stewards of God's creation and as creatures ourselves.

Legend has it that St Francis thanked his donkey at his bedside for carrying and helping him throughout his life, and his donkey wept.