Billy was an enslaved African American born possibly about 1754, perhaps in Richmond County . In 1781 he was part of the estate of John Tayloe (1721–1779), a wealthy planter and member of the governor's Council. When Billy first came into Tayloe's possession is not known, and his parents and other relatives have not been identified.

Billy may have been the runaway slave sought in April 1774 by Thomas Lawson, Tayloe's iron agent at the Neabsco Furnace in Prince William County. Lawson placed a detailed newspaper advertisement to try to recover Billy, described as a former waiting boy, a skilled ironworker, a stonemason, and a miller. Lawson further depicted Billy as an ingenious twenty-year-old man who had the ability to gain "the good Graces of almost every Body who will listen." In 1782 Tayloe's estate included several men named Billy, making it impossible to determine whether the earlier runaway was the man tried for treason in 1781.

The Prince William County Court indicted "Billy, alias Will, alias William" for "feloniously and traitorously" waging war on April 2, 1781, from an armed vessel against the new state of Virginia. Many African Americans joined the British forces, who had offered freedom to slaves willing to serve the Crown, although other blacks actively supported the American cause. Billy pleaded not guilty and testified that he had been forced to board the vessel against his will and had never taken up arms on behalf of the British. On May 8, 1781, however, four of six Prince William County oyer and terminer judges convicted Billy of treason and sentenced him to hang. They placed his value at £27,000 current money.

Within a week of the verdict Henry Lee (1729–1787) and William Carr , the two dissenting judges, and Mann Page , one of Tayloe's executors, argued to Governor Thomas Jefferson that a slave, being a noncitizen, could not commit treason. Lee and Carr wrote that a slave "not being Admited to the Priviledges of a Citizen owes the State No Allegiance and that the Act declaring what shall be treason cannot be intended by the Legislature to include slaves who have neither lands or other property to forfiet." Their argument about citizenship was very similar to one made on March 19, 1767, by Arthur Lee in his influential public letter on slavery directed to Virginia's legislators and published in William Rind 's Virginia Gazette . In Billy's defense Henry Lee and William Carr also contested the evidence used against him. Billy received a gubernatorial reprieve until the end of June, and the legislature pardoned him on June 14, 1781. What happened to him after that is not known.

Billy's treason trial was neither the first nor the last such prosecution of a bondsman during the American Revolution. In Norfolk County in 1778 a slave named Bob faced charges of treason and robbery. Like Billy he pleaded not guilty but received the death sentence, and he may have been hanged. During the same period at least one other slave, a man named Sancho, was found guilty of warlike action against the state and hanged, while still another, Jack, may have escaped execution. Similar judicial actions against supposed treason occurred during times of public peril. In the aftermath of Nat Turner's Rebellion , Southampton County justices in October 1831 heard the charge of treason against Jack and Shadrach, only to dismiss the charge tersely: "a slave cannot be tried in this court for Treason." This exemption of enslaved people from treason prosecutions appears to have prevailed in Virginia during the American Civil War (1861–1865) as well.

Billy made his mark on history because his trial forced white leaders to confront the logic of the peculiar institution. His case was doubly ironic. A slave, he was nevertheless tried for disobeying one of the laws of the commonwealth. Excluded from the protections conferred by citizenship, he was still shielded from execution because Virginia's law of treason could not logically apply to him.