Tinsley Randolph Mercer, a daughter of Dale T. Mercer of Richmond, Va., and George R. Mercer Jr. of Palm Beach, Fla., was married yesterday to Robert Livingston Mortimer, a son of Senga M. Mortimer and John Jay Mortimer of New York. Canon Robert G. Hetherington performed the ceremony at St. Paul's Episcopal Church in Richmond.

The couple, both 26, met as students at the Lawrenceville School in Lawrenceville, N.J.

Mrs. Mortimer graduated from Columbia. She is an account executive in New York at Harrison & Shriftman, a public relations firm. Her mother is an interior designer in Richmond, where the bride's father is a principal in the George-Marshall Corporation, a real estate investment concern.

Mr. Mortimer, who is known as Topper, graduated from New York University. He is a vice president for marketing at the Guggenheim Group, an investment banking concern in New York. His mother is the senior editor at House Beautiful magazine in New York.

The bridegroom is a great-grandson of Henry Morgan Tilford, a president of the Standard Oil Company of California and an early resident of Tuxedo Park, N.Y.; he is also a descendant of John Jay, the first chief justice of the United States.