Gross was accepted by the Redemptorists in 1857 and entered St. Mary's Redemptorist Novitiate and Seminary, Annapolis, Maryland.  He was considered by his seminary classmates as the life of the party during recreation periods, and was a spiritual man devoted to both prayer and studies.

        With the beginning of the Civil War in 1862, the Lincoln government took a hard line on military draft exemptions for seminary students, so the Redemptorists advanced William Gross' class to Holy Orders lest they be drafted.  On September 1, 1862, the seminary class of twenty was given minor orders.  On March 19, 1863, they were advanced to the subdiaconate, to the diaconate the following day, and, on March 21, they were ordained to the priesthood by the aging Archbishop Francis Kenrick of Baltimore in the Redemptorist church of St. Mary at Annapolis.

        Fr. William Gross' first assignment was as chaplain for wounded Union soldiers pouring into the military hospitals of Annapolis, including the U.S. Naval Academy, which had been converted into a hospital.  He also took care of a chapel for Confederate prisoners on the outskirts of Baltimore.

        From 1865 to 1872, Fr. Gross became part of a Redemptorist Mission Band whose chief work was to give parish missions throughout the eastern and southern United States.  They preached, taught, and heard thousands of confessions.  The missions attracted Catholics and non-Catholics, who found the talks by Father Gross to be free from anything offensive and his manner courteous.

        In 1868, Fr. Gross and his fellow Redemptorists were invited by the Bishop of Savannah, Georgia, to help with the moral reconstruction of an impoverished and war-torn South.  In the same year his brother, Fr. Mark Gross, volunteered to help the newly consecrated Bishop James Gibbons in the Vicariate Apostolic of North Carolina.  Father Mark Gross would later be named Bishop of the North Carolina Vicariate in 1880, but would decline the appointment.  Father William Gross would have to return twice to Baltimore in the next three years due to overwork and exhaustion.  But, as soon as he had sufficiently recovered, he immediately returned to Georgia.

        Father Gross continued his parish mission work in Baltimore, New York City, and Boston.  In 1875, while serving as pastor of Our Lady of Perpetual Help Mission, Boston, he was named fifth Bishop of Savannah.  He was consecrated Bishop at age 36 America's youngest bishop.  In 1876, he dedicated the new Cathedral in Savannah and opened a men's college, Pio Nono College, in Macon.

        On March 31, 1885, Pope Leo XIII promoted Bishop Gross to Archbishop of Oregon City.  Archbishop Gross was aware of the vast mission work that lay ahead of him in the Oregon country, but accepted the task because he said that he was a missionary by vocation. In 1885, Oregon had an estimated 10,000 Catholics.

Archbishop Gross was installed as Archbishop of Oregon City, on May 23, 1885.  On October 9, 1887, the newly created Cardinal, James Gibbons of Baltimore, came to Portland to present the Pallium to the new archbishop, stopping in Helena, Spokane, and The Dalles to recognize the small Catholic population of the Northwest.  He was the first American Cardinal to visit the west.

Archbishop Gross dedicated the new cathedral at Southwest Third and Stark Street in Portland on August 15, 1885, and acquired the Catholic Sentinel as property of the Archdiocese.
Click for Coat of Arms

        The following year, 1886, Archbishop Gross established the first archdiocesan community of religious women at Sublimity.  They would later become the Sisters of St. Mary of Oregon.  He also invited the Christian Brothers from San Francisco to staff St. Michael's College Portland, and in 1887 saw the opening of Mt. Angel College staffed by the Benedictine Fathers.  In 1889, St. Anselm's Little Seminary opened at Mt. Angel with fifteen students.  Archbishop Gross visited the various parishes and missions of his far-flung archdiocese by carriage, horseback, train, steamer, and even on foot.  On one such visit to eastern Oregon, he was thrown violently from a buckboard.  He emerged shaken, but unharmed.  He often would be delayed for days because of mud and impassable roads.

        Archbishop William Gross ordained the first native Oregonian, Fr. Arthur Lane, in 1895, the grandson of General Joseph Lane, the first Territorial Governor of Oregon.  In 1894, he invested Fr. Adrian Croquet with the robes of a Domestic Prelate, the Northwest's first monsignor.

        Archbishop Gross invited the Dominican Sisters from San Jose to begin Immaculate Heart School in Portland (1889), which would later become Immaculata Academy and Marycrest High School; presided over the Third Provincial Council of Oregon in 1891; and invited the Dominican Fathers in 1894 to establish Holy Rosary parish in Portland.  He invited the Sisters Adorers of the Precious Blood from St. Hyacinthe, Canada, to establish a monastery for contemplatives on Mt. Tabor in Portland in 1892, and Sisters of Mercy to open St. Agnes Baby Home, a home for working girls, and a home for the aged in 1896.

        Archbishop Gross celebrated the Twenty-Fifth Anniversary of his episcopal consecration April 27, 1898.  As a gift, the priests and people of the Oregon City Archdiocese presented him with a private residence on Southwest Sixteenth Avenue and Davis Street, which no longer stands.

        Archbishop Gross became ill while giving a retreat for Redemptorist students in Annapolis, Maryland, and died shortly afterwards at St. Joseph Hospital in Baltimore on November 14, 1898, at the age of 61.  Cardinal James Gibbons of Baltimore celebrated the Funeral Mass in Baltimore, and Archbishop Gross was buried on November 18 in the Most Holy Redeemer Cemetery in Baltimore.