He remains the longest-serving bishop of the diocese and, during his 30 years in office, he was most notably responsible for building the current Cathedral Basilica of the Assumption.

His first assignment was to St. Peter's Church in Mount Clemens, whose founding pastor was Gabriel Richard (the first Catholic priest to serve in Congress).

When the Diocese of Grand Rapids was erected in 1882, Maes was included on the list of candidates for bishop that was sent to Rome but the title was ultimately given to Henry Richter.

[2] On September 11, 1884, a telegram from Rome announced that Pope Leo XIII appointed Maes to be Bishop of Covington in Kentucky.

In 1890 he purchased property at the corner of Madison Avenue and Twelfth Street, a site that was considered to be the center of the city.

[14] To design the building, he hired a Detroit architect who had worked on St. Anne's Church and based his plans on Notre-Dame de Paris.

He helped organize the Priests' Eucharistic League in the United States, serving as its first national moderator and editor of its monthly publication Emmanuel.

[2] In October 1895 he chaired the first Eucharistic congress in the country at Washington, D.C., which was attended by more than 20 bishops and 300 priests (including Apostolic Delegate Francesco Satolli).

[4] He was elected permanent president of the Eucharistic Congresses in the United States, and participated in the international gatherings at Namur (1902), Metz (1907), Montreal (1910), Vienna (1912), and Lourdes (1914).

In 1914, during his last ad limina visit to Rome, Maes made a stop at his native country and was deeply distressed to see that his childhood home had been destroyed during World War I.