Prince Demetrius Gallitzin was born in The Hague, Holland on December 22, 1770, to Prince Demetrius Gallitzin and Countess Amalie von Schmettau. At the time of Gallitzin's birth, his father was the Russian ambassador to Holland, and had served the previous fourteen years as the ambassador to France. His mother was the only daughter of the revered Prussian Field-Marshal von Schmettau, a decorated officer under Frederick the Great. Very wealthy and influential, Gallitzin's parents enjoyed the company of such famed persons as Diderot, Voltaire, and d'Alembert. The senior Prince Gallitzin was an Orthodox Russian in name, but openly shared his true beliefs. Countess Amalie, however, was baptized in the Catholic Church but largely disregarded her religious education until 1786, when, after a severe illness, she returned to the Church as a fervent Catholic and would remain so until her death in 1806.

Born and baptized in the Greek Orthodox Church, the religious education of young Gallitzin was largely ignored until he chose to convert to Catholicism at age seventeen. To please his mother, whose birth, marriage and First Holy Communion all occurred on August 28, the Feast of St. Augustine, Gallitzin took the name of Augustine for his confirmation and wrote his name as Demetrius Augustine from that day.

Once Gallitzin completed his formal education under the best masters of the day, his father willed that he join the military. He was appointed aide-de-camp to the Austrian general von Lillien in 1792, in the first battles against France. However, Austria soon discharged its foreign officers and Gallitzin was sent home. Without the opportunity to serve and with the present instability of the continent, his parents decided he should travel to the United States. His mother provided him with letters of introduction from the prince-bishops of Hildesheim and Paderborn to Bishop Carroll of Baltimore, and with his tutor, Father Brosius, he embarked on August 18, 1792.

He landed in Baltimore on October 28 of that same year, and changed his name to Augustine Schmettau, to avoid the inconvenience and expense of traveling as a Russian prince. This name was then altered to Smith and he was known as Augustine Smith for many years after. Not long after his arrival, he became engrossed by the needs of the Church in the United States. He decided to become a priest, and entered St. Mary's Seminary in Baltimore as one of its first students. His parents, displeased with his choice, begged him to return home. His father, who had secured him a commission in the Russian army, warned that his decision would deny him succession to the family inheritance.

Such an entreaty had little effect on Gallitzin, who proceeded through the Sulpician seminary and, on March 18, 1795, became the first in the original colonies of the United States to receive all the rites of Holy Orders from tonsure to priesthood. He began his ministry in Baltimore, and in missions in southern Pennsylvania and northern Maryland and Virginia. In 1796, he received a call from an ill Protestant in what was then McGuire's Settlement, located in what is now Cambria County, Pennsylvania. The patient requested his assistance in that she desired to become Catholic before her death. Father Gallitzin went to her and began the process of conversion. While he was there, he visualized the idea of creating a Catholic settlement in the middle of the Allegheny region.

In order to make this idea a reality, Father Gallitzin invested his financial assets in the purchase of four hundred acres of land, and received permission from Bishop Carroll to establish residence there with a jurisdiction whose radius was larger than one hundred miles. In the summer of 1799, he officially began his tenure as the first priest of the Alleghenies. He built an initial log church that measured 44 feet by 25 feet. As the number of Catholics in the area increased, Gallitzin took measures in 1808 to double the capacity of the structure. As the population continued to grow, he tore the log building down in 1817 and replaced it with a frame church, which became the parish church until 1853.

It was upon this foundation that Father Gallitzin named this colony Loretto, after the Marian shrine in Loreto, Italy, as the Virgin Mary is deeply revered in the Catholic faith. In addition to his expansions of the Church, he made it his mission to tend to his followers, creating farms, saw-mills, grist-mills, and tanneries along the countryside and feeding and sheltering those in need. It is estimated that he spent at least $150,000 of his inheritance, a small portion of what he was to receive, under the assumption that he could repay the debt when he came into the funds. This was not to be, however. The Russian government disinherited him for becoming a Catholic and a priest, and the German prince who married his sister spent both his and her inheritance. Through petitions to Bishop Carroll, Pope Gregory XVI and a sympathetic public, Gallitzin was able to keep most of his operations afloat, though he did not repay his full debt until shortly before his death.

Amidst this monetary difficulty, Gallitzin also became aware of general attacks on Catholics by Protestants in the colonies. After a sermon delivered in Huntingdon, Pennsylvania in 1814 by a Protestant minister compared Catholics to heathens and denounced the "popery," Gallitzin became the first in the United States to defend the Church. In response, Gallitzin published his "Defence of Catholic Principles," which was shortly followed by the less known "A Letter on the Holy Scriptures" and "An Appeal to the Protestant Public."

Gallitzin continued to expand his missions in Loretto, hoping to create the town as an Episcopal see. In 1827, he accepted the office of the Vicar-General for Western Pennsylvania, because he felt it could promote the interests of the Church, but rejected proposals for nomination as the first Bishop of Cincinnati and first Bishop of Detroit, wanting to remain close to home.

On May 6, 1840, Gallitzin passed away. He was buried as he wished, midway between his residence and the church he erected, which were approximately thirty feet apart. In 1847, his remains were moved to a vault in a field close to the center of town and a monument was created out of rough mountain stone. In 1891, his remains were placed in a metallic casket and, in 1899, upon the foundation of the Loretto Mission, the former monument was capped by a bronze-statue of Gallitzin, donated by Charles M. Schwab. Schwab also donated funds toward a large stone church in Gallitzin's name, which was consecrated on October 2, 1901.

His legacy has lived on to modern times. Considered by many in the Cambria County region to be the "Apostle of the Alleghenies," there are many tributes to the priest such as the town of Gallitzin, Gallitzin Springs and, most recently, Prince Gallitzin State Park. In 1955, a park plan was proposed in the Killbuck area. According to the Pennsylvania Department of Conservation and Resources, "Governor George M. Leader announced plans for 'Pennsylvania's largest and most complete state park' (on April 4, 1957 ) and land acquisition began." Groundbreaking ceremonies occurred in 1958, and in 1960, Glendale Lake was filled, with boating permitted the following year. On May 29, 1965, Governor Scranton dedicated the park Prince Gallitzin State Park, which was the biggest state park of its kind at the time.

In March 2005, Bishop Joseph V. Adamec of the Diocese of Altoona-Johnstown petitioned the Vatican to consider Father Gallitzin for canonization, or being declared a saint. In a release from June 6, 2005, the Catholic Register of Altoona-Johnstown stated that the "Congregation for Saints of the Holy See recently notified Bishop Joseph that the diocesan process for submitting the name of Father Gallitzin for eventual canonization could continue." An update submitted on October 3, 2005, by Bishop Adamec requested the assistance of parishioners in gathering information about the priest to aid in this process. The influence of the work of Father Gallitzin continues to be revered by Catholic worshippers in the Cambria County area.