Maréchal's tenure as archbishop was marked with conflicts with lay trustees of parishes in Virginia and South Carolina who believed they had the power to appoint their own priests.

The Sulpician Order gave Maréchal his tonsure, a crown-like haircut allowing a seminarian to continue his studies, at the end of 1787.

[1][2] Due to popular unrest in the Paris area, Maréchal left the Saint-Sulpice Seminary for Bordeaux, France, in early 1792.

In 1801, the Sulpicians sent Maréchal to teach philosophy at the new Georgetown College in Washington, D.C.[7] With the ascension of Napoleon Bonaparte as first consul of the new French Republic, it became safer for Catholic clergy to practice in France.

[1][8] Maréchal indicated that the most pressing problems facing the archdiocese were the shortage of priests and overly independent lay parish trustees.

[10] At the same time, the Propaganda Fide in Rome was receiving reports from primarily Irish parishes in Virginia and South Carolina that were unhappy with French priests who were not fluent in English or ignorant of local customs.

He had placed St. Mary's, a primarily Irish parish in that city, under interdict because its trustees had refused to accept a French priest that Neale had appointed as pastor.

Complaining of Lucas' difficulty in conducting mass in English, the board of trustees had finally locked him out of St. Mary's church there.

[6][11] On May 31, 1821, Maréchal dedicated the Cathedral of the Assumption of the Blessed Virgin Mary in Baltimore, which had been started by Archbishop John Carroll in 1806.

[15] Pius VII ruled in Maréchal's favor, but the Jesuits refused to comply with his, contesting ownership of White Marsh for many more years.

A more significant outcome of Maréchal's trip was the pope's agreement to consult with the archbishop of Baltimore on the erection of new dioceses and the appointment of new bishops in the United States.

Kelly wrote about the meeting:He [Maréchal] did not receive me over kindly, and tried to persuade me it would be dangerous to take possession of my See; but his arguments did not satisfy me, and I arrived Norfolk on 19th January.

[6] In 1822, at Maréchal's request, the Vatican designated St. Mary's Seminary as a pontifical university, giving it the authority to grant Doctor of Divinity degrees.

[7][6] With Maréchal gravely ill, the Vatican on January 8, 1828, appointed Reverend James Whitfield as coadjutor archbishop of Baltimore to assist him.