In 1827, at the age of 18, he married 16-year-old Eliza McCardle, the daughter of a local shoemaker. The pair were married by Justice of the Peace Mordecai Lincoln, first cousin of Thomas Lincoln, whose son would become president. The Johnsons were married for almost 50 years and had five children: Martha (1828), Charles (1830), Mary (1832), Robert (1834), and Andrew Jr. (1852). Though she had tuberculosis, Eliza supported her husband's endeavors. She taught him mathematics skills and tutored him to improve his writing.[14][15] Shy and retiring by nature, Eliza Johnson usually remained in Greeneville during Johnson's political rise. She was not often seen during her husband's presidency; their daughter Martha usually served as official hostess.[16]
Johnson's tailoring business prospered during the early years of the marriage, enabling him to hire help and giving him the funds to invest profitably in real estate.[17] He later boasted of his talents as a tailor, "my work never ripped or gave way".[18] He was a voracious reader. Books about famous orators aroused his interest in political dialogue, and he had private debates on the issues of the day with customers who held opposing views. 