As a missionary in North America, Lamy served at several missions in Ohio and Kentucky when, to his surprise, he was notified that Pope Pius IX was appointing him as bishop of the recently created Apostolic Vicariate of New Mexico on July 23, 1850.
 At the same time, he was appointed Titular Bishop of Agathonice.
 He was consecrated a bishop on November 24, 1850 by Archbishop Martin Spalding of Louisville; Bishops Jacques-Maurice De Saint Palais of Vincennes and Louis Amadeus Rappe of Cleveland served as co-consecrators.
 After an arduous journey on primitive transportation, Lamy reached Santa Fe in the summer of 1851.

Lamy entered Santa Fe on 9 August 1851, and was welcomed by the Governor of the territory, James S. Calhoun, and many other citizens.
However, Juan Felipe Ortiz, a Spanish priest who was responsible for administration of the Catholic Church in New Mexico, told Lamy that he and the local clergy did not recognize his authority and would remain loyal to Bishop José Antonio Laureano de Zubiría of the Diocese of Durango, Mexico, who had visited Santa Fe just a few months before.
 Lamy wrote to Zubiría asking him to explain the change of responsibility to the New Mexico priests.
When his request was unanswered, he went in person to Durango to meet with Zubiría, showing him the papal document that appointed Lamy.
In light of this, Zubiría had to agree to inform the priests of the change.

On July 23, 1853, the Vicariate of New Mexico was raised to the Diocese of Santa Fe, and Lamy was appointed its first bishop.
 His early efforts as bishop were directed to reforming the New Mexico church, the building of more churches in the territory, the creation of new parishes, and the establishment of schools.
He ended the practice of concubinage widely practiced by the local priests and he suppressed religious brotherhood societies within individual communities.
He participated in the First Vatican Council from 1869-1870.

Lamy was responsible for the construction of the Cathedral Basilica of Saint Francis of Assisi (commonly known as St. Francis Cathedral) and Loretto Chapel.
 Both churches were built in French styles familiar to Lamy — the Cathedral is Romanesque Revival, while the Chapel is Neo-Gothic.
 On February 12, 1875, the Diocese of Santa Fe was elevated to an archdiocese with Lamy as its first archbishop.
 On May 1, 1885, Lamy consecrated Peter Bourgade as bishop; Bourgade would later become the fourth Archbishop of Santa Fe.

Lamy ended his tenure as bishop when he resigned in 1885.
He was appointed Titular Archbishop of Cyzicus later that year.
As a missionary in North America, Lamy served at several missions in Ohio and Kentucky when, to his surprise, he was notified that Pope Pius IX was appointing him as bishop of the recently created Apostolic Vicariate of New Mexico on July 23, 1850.  At the same time, he was appointed Titular Bishop of Agathonice.  He was consecrated a bishop on November 24, 1850 by Archbishop Martin Spalding of Louisville; Bishops Jacques-Maurice De Saint Palais of Vincennes and Louis Amadeus Rappe of Cleveland served as co-consecrators.  After an arduous journey on primitive transportation, Lamy reached Santa Fe in the summer of 1851.
Lamy entered Santa Fe on 9 August 1851, and was welcomed by the Governor of the territory, James S. Calhoun, and many other citizens. However, Juan Felipe Ortiz, a Spanish priest who was responsible for administration of the Catholic Church in New Mexico, told Lamy that he and the local clergy did not recognize his authority and would remain loyal to Bishop José Antonio Laureano de Zubiría of the Diocese of Durango, Mexico, who had visited Santa Fe just a few months before.  Lamy wrote to Zubiría asking him to explain the change of responsibility to the New Mexico priests. When his request was unanswered, he went in person to Durango to meet with Zubiría, showing him the papal document that appointed Lamy. In light of this, Zubiría had to agree to inform the priests of the change.
On July 23, 1853, the Vicariate of New Mexico was raised to the Diocese of Santa Fe, and Lamy was appointed its first bishop.  His early efforts as bishop were directed to reforming the New Mexico church, the building of more churches in the territory, the creation of new parishes, and the establishment of schools. He ended the practice of concubinage widely practiced by the local priests and he suppressed religious brotherhood societies within individual communities. He participated in the First Vatican Council from 1869-1870.
Lamy was responsible for the construction of the Cathedral Basilica of Saint Francis of Assisi (commonly known as St. Francis Cathedral) and Loretto Chapel.  Both churches were built in French styles familiar to Lamy — the Cathedral is Romanesque Revival, while the Chapel is Neo-Gothic.  On February 12, 1875, the Diocese of Santa Fe was elevated to an archdiocese with Lamy as its first archbishop.  On May 1, 1885, Lamy consecrated Peter Bourgade as bishop; Bourgade would later become the fourth Archbishop of Santa Fe.
Lamy ended his tenure as bishop when he resigned in 1885. He was appointed Titular Archbishop of Cyzicus later that year.
Jean-Baptiste Lamy