Lyons was born in Ireland about 1734. He graduated from Trinity College Dublin. Following this, he came to King William County, Virginia, and studied law under his uncle, James Power. He was admitted to the bar on February 5, 1756, and started to practice law in the county courts.

On October 20, 1779, Lyons was elected to the general court, which made him an ex officio member of the Court of Appeals. In 1788, the Court of Appeals was reorganized and the judges, reduced to five in number, were to be elected by a joint ballot of both Houses of Assembly. The first five, elected on December 24, 1788, were Edmund Pendleton, John Blair Jr., Peter Lyons, Paul Carrington and William Fleming. Peter Lyons was elected from Hanover County. In 1789, John Blair left the Virginia Court to become a justice of the Supreme Court of the United States. This left Peter Lyons the second ranking member of the Virginia Court of Appeals, which he presided over in the absence of Pendleton. When Pendleton died in 1803, Lyons succeeded him as president, running a court with just three of the original five justices.^[1] Lyons maintained the position of president and chief justice until his death six years later in Hanover County on July 30, 1809.^[2]

• T. Nicholson, "Cases Decided in the Supreme Court of Appeals of Virginia," Volume 6. Virginia. Supreme Court of Appeals (1854)
• R.F. Walker, "Calendar of Virginia State Papers and Other Manuscripts: ... Preserved in the Capitol at Richmond," Volume 4. (Virginia, 1884), p. 662
• "Journal of the Senate of Virginia", Virginia. General Assembly. Senate Commonwealth of Virginia (1828) p. 7