Brearly (Brearley) was descended from a Yorkshire, England, family, one of whose members migrated to New Jersey around 1680. Signer Brearly was born in 1745 at Spring Grove near Trenton, was reared in the area, and attended but did not graduate from the nearby College of New Jersey (later Princeton). He chose law as a career and originally practiced at Allentown, NJ. About 1767 he married Elizabeth Mullen.