Hammond "secured his financial independence" by marrying Catherine Elizabeth Fitzsimmons, who was a shy, plain 17-year-old with a substantial dowry. He became a wealthy man through this marriage and entered the planter class.

Hammond rejected any government encroachment on slaveholding, even in wartime. When the South Carolina government requisitioned 16 of his slaves to improve fortifications for Charleston, he refused, calling it "wrong every way and odious." Also, when a Confederate army officer stopped by to requisition some grain, he tore up the requisition order, tossed it out a window, and wrote about it that it compensated him too little, and that it was like "branding on my forehead: 'Slave'".

Giving some of the grain my slaves harvested to an army that's protecting my rights to own slaves is the same exact thing as being a slave.

CW: Sexual violence

Hammond's Secret and Sacred Diaries (not published until 1989) described, without embarrassment, his sexual abuse over two years of four teenage nieces, daughters of his sister-in-law Ann Fitzsimmons and her husband Wade Hampton II. He blamed his behavior on what he described as the seductiveness of the "extremely affectionate" young women. The scandal "derailed his political career" for a decade to come after Wade Hampton III publicly accused him in 1843 when Hammond was governor. He was "ostracized by polite society" for some time, but in the late 1850s, he was nonetheless elected by the state legislature as a U.S. senator.

Hammond was known to have repeatedly raped two female slaves, one of whom may have been his own daughter. He raped the first slave, Sally Johnson, when she was 18 years old.

Later, Hammond raped Sally Johnson's daughter, Louisa, who was a year old baby when he bought her mother; the first rape apparently occurred when Louisa was 12; she also bore several of his children.