Thomas Haight Leggett, American consulting mining engineer, was the son of Charles Pleasants Leggett and his wife Ellen, born Currie. He qualified at the Columbia University School of Mines, New York city, in 1879. He subsequently worked in different positions in several countries: As assistant engineer for the New York River and Harbour Surveys (1880); superintendent of mining properties in the Batopilas district, Chihuahua, Mexico (1881-1883); visiting mining camps in the western United States (1884); mining engineer to the New York and Honduras Rosario Mining Company at San Juancito, Honduras (1884-1887); manager of Mudsill Mining Company, Fairplay, Colorado (1888); general manager of Darien Gold Mining Company of Cana, Colombia (1889-1890); and president and mamager of Standard Consolidated Mining Company (1891-1895). In 1889 he contributed "Notes on the Rosario mine at San Juacinto, Honduras" to the Transactions of the American Institute of Mining Engineers, followed by "A twelve-mile transmission of power by electricity" (Ibid, 1895). In 1894 he compiled a report for the State Mineralogist of California on Electric power transmission plants and the use of electricity in mining operations..., which was published in Sacramento, California.
In July 1895 Leggett was appointed consulting engineer to S. Neuman and Company of London and Johannesburg. Through this company Sigismund Neuman (1857-1916) controlled several of the most important mines on the Witwatersrand. Leggett appears to have been stationed mainly in London. However, in May 1898 he became a member of the South African Association of Engineers and Architects. In September that year he published an article on "Diamond mining in South Africa" in Cassiers Magazine. A more important contribution followed in 1902, when, with F.H. Hatch* as co-author, he wrote "An estimate of the gold production and life of the Main Reef Series, Witwatersrand, down to 6000 feet". The paper was read before the (British) Institution of Mining and Metallurgy in October 1902 and published both in its Transactions (Vol. 10) and as a pamphlet. He retained an interest in the South African gold mines for some years afterwards, reporting on "Present mining conditions on the Rand" to the American Institute of Mining Engineers in 1908.
Leggett was married to Fannie Borrowe, with whom he had three sons.