He was born on Newington Plantation in King and Queen County, Virginia and educated at the William and Mary. He married a wealthy heiress named Judith Robinson at the age nineteen, but she died two years later, leaving him two daughters.
He journeyed to England for two years and returned to the colonies in 1760, marrying again, this time to Elizabeth Corbin, and represented King William County in the Virginia House of Burgesses. He joined the patriot's Committee of Safety in Virginia in 1774 and represented his county in the Virginia Convention.
When Peyton Randolph died in 1775, Braxton was appointed to take his place in the Continental Congress. He served in the Congress from February 1776 until August, when Virginia reduced its delegation to five members. Afterwards he returned to the House of Burgesses, and later served on the State's Executive Council.