An Irishman by birth, he was one of the twelve disciples who accompanied St. Columbanus to Gaul, and established themselves with him at Luxeuil. Gall again followed his magister, in 610, on his voyage on the Rhine to Bregenz; but he separated from him in 612, when Columbanus left for Italy; and he remained in Swabia, where, with several companions, he led the life of a hermit, in a desert to the west of Bregenz, near the source of the river Steinach. There, after his death, was erected an "ecelesia Sancti Galluni" governed by a "presbyter et pastor". Before the middle of the eighth century this church became a real monastery, the first abbot of which was St. Otmar. The monastery was the property of the Diocese of Constance, and it was only in 818 that it obtained from the Emperor Louis the Pious the right to be numbered among the royal monasteries. and to enjoy the privilege of immunity. At last, in 854, it was freed from all obligation whatever towards the See of Constance, and henceforth was attached only by ties of canonical dependence. Called "Abbey of St. Gall", not from the name of its founder and first abbot, but of the saint who had lived in this place and whose relics were honoured there, the monastery played an illustrious part in history for more than a thousand years.
Apart from this authentic history, there exists another version or tradition furnished by the Lives of St. Gall, the most ancient of which does not antedate the end of the eighth century. A portion of the incidents related in these Lives is perhaps true; but another part is certainly legendary, and in formal contradiction to the most ancient charters of the abbey itself. According to these biographies, Gall was ordained a priest in Ireland before his departure for the Continent, therefore before 590. Having reached Bregenz with Columbanus, he laboured in the country as a missionary, and actively combated the pagan superstitions. Prevented by illness from following Columbanus to Italy, he was placed under interdict by the displeased Columbanus, and in consequence could not celebrate Mass until several years later, after the death of his old master. Gall delivered from the demon by which she was possessed Fridiburga, the daughter of Cunzo and the betrothed of Sigebert, King of the Franks; the latter, through gratitude, granted to the saint an estate near Arbon, which belonged to the royal treasury, that he might found a monastery there. Naturally the monastery was exempt from all dependence on the Bishop of Constance; moreover, Gall twice refused the episcopal see of that city, which was offered to him, and having been instrumental in securing the election of a secular cleric, the deacon John, the latter and his successors placed themselves in every way at the service of the abbey. Gall also declined the abbatial dignity of Luxeuil, which was offered him by the monks of the monastery after the death of St. Eustace. Shortly afterwards he died, at the age of ninety-five, at Arbon, during a visit; but his body was brought back to the monastery, and God revealed the sanctity of his servant by numerous miracles. His feast is celebrated on 16 October, the day ascribed to him in some very ancient martyrologies, while Adon, it is not known for what reason, makes it occur on 20 February. The saint is ordinarily represented with a bear; for a legend, recorded in the Lives, relates that one night, at the command of the saint, one of these animals brought wood to feed the fire which Gall and his companions had kindled in the desert.
The most ancient Life, of which only fragments have been discovered till the present date, but otherwise very important, has been remodeled and put in the better style of the ninth century by two monks of Reichenau: in 816-24 by the celebrated Wettinus, and about 833-34 by Walafrid Strabo, who also revised a book of the miracles of the saint, written somewhat earlier by Gozbert the Younger, monk of St. Gall. In 850 an anonymous monk of the same abbey wrote, in verse, a Life which he published under the name of Walafrid; and others after him further celebrated the holy patron in prose and verse.