Thomas Macomb Flandrau was born on July 8, 1826, in New York City to Thomas Hunt Flandrau and Elizabeth Macomb. His father was a lawyer who owned $1,500 of real estate by 1850. Flandrau grew up and attended school in Washington, D.C., and he graduated from the National Medical College in March 1848. He returned to his parents’ household in Whitestown, New York, around 1849 and worked as a physician there. He married Clarissa Foote sometime in the 1850s, and they had at least three children: Elizabeth, born around 1859; Ruth, born around 1863; and Julia, born around 1872. By the early 1860s, he was living in Rome, New York.
Flandrau received a commission as a surgeon of the 146th New York Infantry on August 25, 1862. He supported the Democratic Party and opposed emancipation as late as December 1862. Nonetheless, he remained steadfastly loyal to the Union. As he explained during the winter of 1862-63, his political beliefs were to “whip the rebs first & dispose of the [negroes] afterwards.” His regiment took part in the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, the siege of Petersburg, and the Appomattox campaign. He mustered out in Washington, D.C., on July 6, 1865.
He returned to Rome after the war and resumed his medical practice. By 1870, he owned $7,000 of rea estate and $3,000 of personal property. His practice flourished, and by 1880, he employed at least three servants. Flandrau joined the Oneida County Medical Society and the American Medical Association, and he attended Internal Medical Congresses across Europe. He died in Rome, New York, on August 8, 1898.