Bradley's early youth was spent with his grandparents in Cheshire, Connecticut, but he fitted for college at Charlestown, New Hampshire. During his freshman year at Yale he was expelled for a prank for which he was not responsible though he later said he was guilty of other similar acts.
Upon his return home from college at Charlestown, his disgusted father gave him a dung fork and set him to work at a manure heap. But he retrieved himself by deciding to become a lawyer, studying with Judge Simeon Strong of Amherst, then with a Mr. Ashmun of Blandford, Massachussets, and later returning to his father's office to complete his studies. At seventeen he delivered the Fourth of July oration at Westminster, the program including an ode he had written.
At eighteen William Bradley became secretary of the commissioner of bankruptcy of Westminster. Admitted to the bar when but twenty (1802), because of his youth he was refused permission to practise before the supreme court of the state, but the legislature made him attorney for Windham County, thus giving him access to the supreme court. In 1806-07 he represented Westminster in the Vermont legislature.
In 1812 he was a member of the Governor's Council which preceded the present state Senate. He was twice a representative in Congress--in 1813-15, when he was an ardent supporter of Madison's war policy, and again in 1823-27. A quarrel with John Quincy Adams, which turned him to the support of Jackson, caused his retirement from public life at Washington, when but forty-five. What he himself considered his greatest public service was the surveying, as agent of the treasury department, under the Treaty of Ghent, of the northeastern boundary between the United States and Canada. In this work he spent five years (1817 - 22), and though Great Britain at first rejected this line it was finally adopted by the Ashburton Treaty.
After his retirement from national affairs and his return to the practise of law he continued within the state of Vermont to be the actual leader of Jacksonian democracy and almost its perpetual candidate for governor. In 1857 he was a member of the state constitutional convention.
In 1858 he took formal leave of the bar after fifty-six years of practise. He seems to have more enjoyed leading the uphill fight of Vermont democracy than the actual holding of public office, and his relish of the contest was said to be in inverse proportion to his chance of being elected.
In 1848 Bradley joined the Free-Soil party and in 1850 was a member of the state legislature. Later he was a member of the young Republican party, heading the Frémont electoral ticket in 1856.
When Bradley was two years old, his hearing was impared by scarlet fever.
At the age of twenty William Czar Bradley married Sarah Richards, daughter of Hon. Mark Richards of Westminster who was lieutenant-governor of Vermont.