Thaddeus Roberts was born around 1838 in New York to George and Hope Roberts. His father was a spinner who owned $500 of real estate by 1850. Roberts grew up and attended school in Seneca Falls, New York.
He enlisted in the Regular Army on July 19, 1858, and he mustered out on March 1, 1862. He returned to the Union army on September 14, 1862, receiving a commission as a 1st lieutenant in Company A of the 148th New York Infantry. The regiment took part in the Battle of Cold Harbor and the siege of Petersburg. He was promoted to captain on January 31, 1865, and he resigned on May 15, 1865.
He returned to the Regular Army after the war, serving as a private in one of the Engineer Battalions. He was stationed in New York Harbor from August 1865 until March 1867. He was promoted to 2nd lieutenant in the 23rd United States Infantry in early 1867, and he was stationed in Oregon. He died sometime in 1877.