Thomas Egleston was born on December 9, 1832, in New York, New York.

He was an American engineer. In 1854, he graduated from Yale University and continued his studies in École nationale supérieure des mines de Paris in 1860. He pursued his interest in geology and chemistry and attended lectures at the Jardin des Plantes of Paris. After leaving Paris, Egleston travelled extensively in France and Germany to study geological collections. On his return to America, he got employed by the Smithsonian Museums in Washington D.C. In 1864, he founded the School of Mines of Columbia University and became its first professor of mineralogy and metallurgy, a position he held until his death in 1900. In 1866, he was commissioned to make a geological survey of the then-developing Union Pacific Railroad and examine fortifications in 1868. He was a regular government advisor on topics of furnace construction and the treatment of ores. In 1874, Egleston received an honorary degree of Ph.D. from Princeton and LL.D. from Trinity College. He was a member of the National Academy of Sciences and vice-president of the New York Academy of Sciences. He also served as president of the American Institute of Mining Engineers. He was a prominent author of scientific works and an owner of numerous metallurgical patents. He published a biography of his grandfather “The Life of John Paterson: Major-General in the Revolutionary Army” (1898).

In 1865, he married Augusta McVickar (1828–1895). He died on January 15, 1900, in New York, New York.