At age 17, he was brought to the United States by his uncle Jean Chapelle, a missionary priest in Haiti who worked on the Vatican's concordat with the Haitian government and was on the eve of being appointed Archbishop of Port-au-Prince before his death in 1861.

His educational pursuits led his parishioners in Rockville to petition Archbishop Spalding for a new pastor, complaining that Chapelle was "invisible during the week and incomprehensible on Sundays.

[3] He was instrumental in organizing the Catholic University of America, purchasing the land where it still stands and recruiting President Grover Cleveland to attend the laying of the cornerstone in 1888.

He received his episcopal consecration on the following November 1 from Cardinal James Gibbons, with Archbishop Salpointe and Bishop John Joseph Kain serving as co-consecrators, at the Cathedral of Baltimore.

[3] In civic affairs, Chapelle was an early supporter of the cause for New Mexico's statehood (which would be accomplished in 1912), saying in 1894, "As it is, we have no voice in the election of governor, judges or any other officials of importance, and we think we have a right to this.

[6] Over the course of his tenure, he succeeded in finally paying off the debt that had long plagued the Archdiocese of New Orleans, which had fallen from $590,000 when he visited with Cardinal Gibbons in 1885[9] to $135,000 when he assumed charge in 1898.

Due to his prolonged absences from New Orleans, he received Gustave Augustin Rouxel as an auxiliary bishop in February 1899 to tend to the archdiocese's pastoral needs.

[18] Under the treaty, which was signed on December 10 that year, Spain ceded the heavily Catholic colonies of Cuba, Puerto Rico, and the Philippines to the United States.

[18] Chapelle visited Cuba and Puerto Rico in early 1899 to report on the Church's conditions there and suggest a plan for reorganization.

This helped fuel the Philippine Revolution, during which the friars were driven from their churches and their property was confiscated by Emilio Aguinaldo and his fellow revolutionaries.

However, he met resistance from General Elwell Stephen Otis, the military governor of the Philippines, who believed that reinstating the friars would get them killed and usually turned any recovered Church property over to local civil authorities.

[20] Chapelle protested this policy, accusing General Otis' advisers of being "animated with a narrow-minded spirit of hostility to the Catholic Church, whilst they should look at the question presented to them from a disinterested and American point of view.

"[20] Chapelle's refusal to compromise on the issue of the friars' land cost him a good deal of political influence.

"[9] Before departing his post, Chapelle wrote to Taft to declare the commission "has taken, unconsciously perhaps, indirectly surely, a hostile attitude towards the Catholic Church and her interests.

"[3] Nevertheless, after Chapelle departed for Rome in April 1901 to report on his mission, he was relieved of his duties in the Philippines and was replaced by Donato Sbarretti.