Robert Lincoln graduated from Phillips Exeter Academy, then studied at Harvard University from 1861 to 1864 following which he enrolled in Harvard Law School. However, he did not graduate and in 1865 joined the Union Army. He held the rank of Captain, serving in the American Civil War as part of General Ulysses S. Grant's staff.
Following his father's assassination, in May of 1865 he, his brother Thomas (Tad) Lincoln (1853-1871), and their mother moved to Chicago where Robert completed his law studies at the University of Chicago. He was admitted to the bar on February 25, 1867. The following year he married Mary Eunice Harlan (1846-March 31, 1937), the daughter of Senator James Harlan and Ann Eliza Peck of Mount Pleasant, Iowa. They had two daughters and one son:
Robert Todd Lincoln died at his Manchester, Vermont home on July 26, 1926 and was later interred in Arlington National Cemetery next to his wife Mary and their son Jack who died of blood poisoning at the age of 16 in London, England.