William T. Dunn was born in Mercer County, PA, in 1825 to James and Maria (Thompson) Dunn. William received his education in the Mercer County public schools and, in 1852, graduated from Allegheny College, Meadville, PA.
Upon graduating from college, he went to Louisiana and taught school for three years. He returned to Western Pennsylvania in 1856 and in July 1857, began to read law under Judge Wilson McCandless. In 1860, he was admitted to the bar in Allegheny County, practicing law until 1867.
He changed careers, associating with the late Edward Allen as contractors and builders of sewers. On April 25, 1861, he married Mr. Allen's daughter, Amelia Frances. In 1884, he purchased a property in Emsworth. They had one child, a daughter, Amelia Marie. The Dunn's were members of the Methodist Episcopal church.
Mr. Dunn was associated with William T. Dunn and Company which sold building supplies; specializing in terra cotta sewer pipe and cement, with offices at 41 Federal Street.
Mr. Dunn had many connections with other members of the South Fork Fishing and Hunting Club. For instance, he served on the Committee of Public Safety in the aftermath of the Pittsburgh Riot of 1886, with Joseph Horne (Durbin Horne). He served on the board of directors of the American Insurance Company of Pittsburgh, along with Club member James S. McCord. He was named an honorary member of the Hampton Battery Veterans' Association.
In addition to the South Fork Fishing and Hunting Club, Mr. Dunn was a member of the exclusive Linden Club located on Boulevard Place, as were Club members Henry Clay Frick, H.P. and J.L. McClintock, Andrew Mellon, J.E. Schwartz, Henry K. Thaw, and W.K . Woodwell. There was a W.L. Dunn listed as a charter member of the South Fork Fishing and Hunting Club, though it is uncertain if this was just a typographical error of "W.T."