| District: | 9th |
| State: | New York |
| Term: | March 4, 1825 – March 3, 1827 |
| Predecessor: | James L. Hogeboom |
| Successor: | John D. Dickinson |
| Birth Name: | William Telemachus McManus |
| Birth Date: | 28 November 1780 |
| Birth Place: | Brunswick, New York |
| Death Place: | Brunswick, New York |
| Occupation: | Lawyer |
William Telemachus McManus (November 28, 1780January 18, 1835) was an American lawyer and politician from New York.
He was the son of Hugh McManus (1747–1826) and Mary McManus (1751–1834). He attended Lansingburgh Academy. Then he studied law with John Bird, was admitted to the bar, and commenced practice in Troy, New York. He married Catharina Coons, and they had four children, among them Jane (McManus) Cazneau (1807–1878). He was Surrogate of Rensselaer County from 1815 to 1818, and District Attorney from 1818 to 1821.
McManus was elected as an Adams man to the 19th United States Congress, holding office from March 4, 1825, to March 3, 1827. Afterwards he resumed the practice of law.
In 1832, McManus ventured into land speculation, and was one of the founders of the Galveston Bay and Texas Land Company. The next year, he set out with his son Robert, his daughter Jane and a company of German settlers for Texas, which was then still part of Mexico. The scheme failed when the German settlers refused to go beyond Matagorda, and McManus returned with his daughter to Brunswick, NY, in 1834, and died there soon after. His son Robert remained in Texas and became a wealthy planter.