Shortly after his arrival in New York City, he worked as a journeyman baker in Frankfort Street and later started a successful bakery in the same area.
During the 1840s, he contained contracts on the Hudson River Railroad and spent two years building several sections of railway track.
[2] Devlin amassed a large personal fortune through this business and, at his height, was believed to be the largest contractor engaged in city works.
He also became a noted bondsman, providing bail for such figures as Boss Tweed and Henry W. Genet, the latter bringing him to national attention during his criminal trial in 1872–73.
Devlin died from pneumonia at his East Fifty-Seventh Street home on the afternoon of February 1, 1881, and was buried in the family vault at Calvary Cemetery.