He was the first Bishop of Brooklyn, of the United States. state of New York (1853–1891). Early He received his early education at The Albany Academy, and entered the college of Chambly in Quebec, Canada, at age fourteen. After three years at Chambly, he returned to the United States and enrolled at Mount Saint Mary"s Seminary in Emmitsburg, Maryland.
He was ordained to the priesthood by Bishop John Hughes on October 18, 1840.
He then served as a curate at Saint John"s Church in Utica until 1841, when he was transferred to Saint Patrick"s Cathedral in New York City. In 1850, he was named vicar general of the Archdiocese of New New York
On June 19, 1853, Loughlin was appointed the first Bishop of the newly erected Diocese of Brooklyn by Pope Pius IX. He received his episcopal consecration on the following October 30 from Archbishop Gaetano Bedini, with Bishops John McCloskey and Louis Amadeus Rappe serving as co-consecrators. During his 38-year-long tenure, he erected 125 churches and chapels, 93 parochial schools, two colleges, 10 orphanages, five hospitals, two homes for the aged, a home for destitute boys, and a seminary.
The Catholic population of the diocese also increased from about 15,000 to nearly 400,000.
In 1861, he expressed his support for the Union during the Civil War. He attended the Plenary Councils of Baltimore (1852, 1866, 1884) as well as the First Vatican Council (1869–1870) in Rome, where he was named an Assistant at the Pontifical Throne. Loughlin died at his residence in Brooklyn, aged 74.