Born in New York City, Moses Mordecai was the first of Jacob and Judith Myers Mordecai’s six children. When he was a small child relocated to Virginia, and then moved again before he was ten, settling in Warrenton, North Carolina. Soon after their arrival, Moses’s mother died in childbirth and his father remarried to her half-sister; another seven siblings would follow, including brother Alfred. Although his father worked for years as a tobacco merchant, he truly found his calling in 1808, at the age of forty-six, when opened a school, the Warrenton Female Seminary. It developed a reputation for being innovative and rigorous, and the family’s love of learning was not lost on its eldest son.

Educated primarily by his parents, and to a large extent self-taught, Mordecai received some legal training from Judge Oliver Fitts of Warren County, North Carolina. In 1807 he obtained a license to practice law in North Carolina, he became ciruit-riding lawyer in Nash, Franklin, and Northampton counties. The following year, he took over Judge Fitts’s law practice when was appointed attorney general, and Mordecai’s circuit expanded to include Mordecai’s circuit expanded to include Johnston, Wayne, Halifax, Pitt, and Edgecombe counties, as well as superior courts in Raleigh and New Bern. In 1811 he accepted a position as engrossing clerk in the state house of representatives, responsible for editing bills and measures.

By 1812 Mordecai had also become very involved with freemasonry in Raleigh and was a member of Hiram Lodge No. 40. As his law practice grew, his brother Samuel guided him in several lucrative investments, and he began acquiring land and slaves.

On December 9, 1817, Mordecai married Margaret Lane at the home of her grandfather Major John Hinton in Wake County. With this marriage Mordecai came into possession of the Henry Lane House, built in 1785 as a wedding gift for her father, who had died in 1797. Outside of what was then the city limits, the house sat in the middle of a three-thousand-acre plantation, where fourteen enslaved people lived and worked. Mordecai would expand this property, which would come to be known as the Mordecai House; it still stands and is still known as such today, operated by the city of Raleigh.

Moses and Margaret had two children, Henry and Ellen, and when Margaret died, in 1821, he, like his father before him, married the sister of his deceased wife. He had one further child by Anne Willis Lane Mordecai.