Admitted to the Virginia bar, Lomax began practicing law at
Port Royal, Virginia, the Caroline County seat. He moved to
Fredericksburg, the city which had the appellate court for the region, in 1805. In 1809 he settled at
Menokin plantation on Virginia's Northern Neck, which his grandfather had built for another daughter in Westmoreland County, where he remained nine years. In the
War of 1812, he served as a colonel in the U.S. Army. In 1830, the Virginia General Assembly unanimously elected Lomax to the circuit court of the state. Upon Virginia's adoption of a new
Constitution in 1851, legislators again chose Lomax as the judge of the circuit, though he did not seek another term after the expiration of that six year term. The convention that framed this constitution had adopted a clause disqualifying any person over seventy years of age from holding the office of judge; but at the request of members of the bar this provision was cancelled so as not to exclude Lomax. Lomax wrote
Digest of the Laws respecting Real Property generally Adopted and in Use in the United States (3 vols., Philadelphia, 1839; 2nd edition, revised and enlarged, Richmond, 1856) and a
Treatise on the Law of Executors and Administrators generally in Use in the United States (2 vols., 1841; 2nd ed., Richmond, 1856). He continued on the bench until his resignation in December 1856, when he retired to private life. ==Personal life==