Roger Mompesson was born in 1662 in Dorset, England. He was educated at Oxford University, admitted to Lincoln's Inn and was called to the Bar in 1685. He became Recorder of Southampton and was twice elected to the English parliament.
Mompesson arrived in Pennsylvania in February 1704. He was appointed to the Governor's Councils in Pennsylvania, New York and New Jersey and to high judicial office in those three jurisdictions. Mompesson became Chief Judge of the Province of New York on July 15, 1704 and Chief Judge in New Jersey on November 17, 1704. Later, on April 17, 1706, he became Chief Justice of Pennsylvania, although it is not clear that he ever presided in that court. In 1710, he either resigned or was removed as Chief Judge of New Jersey. He continued to hold the office of Chief Judge of New York until his death in March 1715. Mompesson is credited with preparing the first abridgment of the laws of the Province of New York. Historian James Sullivan considered Mompesson the most capable jurist of his time, and the first to bring English forms of procedure into the Province. E. B. O'Callaghan, compiler of Documents Relative to the Colonial History of the State of New York argued that Mompesson "did more than any other man to mould the judicial system of both New York and New Jersey."
Mompesson was one of the grantees of the Little Nine Partners Patent, consisting of lands in Dutchess County, including the towns of Milan and Pine Plains. The patent was confirmed by Queen Anne on September 25, 1708.
Afinogenov, Gregory. "Lawyers and Politics in Eighteenth-Century New York." New York History 89.2 (2008).
Hamlin, Paul M., and Charles E. Baker. Supreme Court of Judicature of the Province of New York, 1691-1704. New York, 1959.