Thomas H. Beddall, a lawyer who for 31 years was the in-house counsel, personal adviser, principal administrative assistant and gatekeeper for philanthropist Paul Mellon, died Sept. 3 at his home in the Fauquier County community of Paris. He was 91.

The cause was myelodysplastic syndrome, a form of anemia, said his daughter Katherine Beddall.

For three decades, Mr. Beddall helped Mellon, one of the leading philanthropists of the 20th century, on projects ranging from the acquisition of 1,864 acres of land that became Sky Meadows State Park in Fauquier County to construction of the West Wing of the Virginia Museum of Fine Arts in Richmond, where the collections of Paul and Bunny Mellon are housed.

On the national and international stage, Mr. Beddall played a key role in arranging funding for construction of the Yale Center for British Art in New Haven, Conn. He negotiated Mellon’s acquisition of the library of the English philosopher John Locke whose 17th-century writing influenced the U.S. Declaration of Independence. The library was later transferred to Britain’s Oxford University.

Mr. Beddall also helped Mellon in the planning for Cape Cod National Seashore and the federal protection of 8,600 acres of Cumberland Island in Georgia. He had no involvement with Mellon’s contributions to the National Gallery of Art in Washington, the philanthropic activity with which the Mellon family is best known.

Thomas H. Beddall, right, poses with philanthropist Paul Mellon at the Virginia Museum of Fine Arts in Richmond. The museum houses the collections of Paul and Bunny Mellon. (Family Photo)

Thomas Henry Beddall was born April 24, 1922, in Pottsville, Pa. He graduated from Phillips Academy in Andover, Mass., and was a 1944 graduate of Yale University. He served in the Army in the Philippines during World War II. In 1950, he received a law degree from the University of Virginia.

He began his legal career with the New York law firm of Sullivan and Cromwell. Mellon hired him in late 1957, partly on the recommendation of a senior partner at the law firm. Mr. Beddall, then a young associate, had encountered the partner by chance in 1952 at the Louvre in Paris, standing in front of Leonardo da Vinci’s “Mona Lisa.”

When Mellon, a longtime trustee at the National Gallery of Art, came looking for an assistant, the partner knew just the man to recommend.

As Mellon’s top adviser, Mr. Beddall specialized chiefly in the activities that most interested his employer: the arts, higher education, the environment and, of course, horses. Mr. Beddall was a trustee and executive vice president of the National Museum of Racing in Saratoga Springs, N.Y., where Mellon went every August for the annual thoroughbred horse races.

Mr. Beddall retired in 1989 but continued to do occasional consulting work for the Mellon family for years. Paul Mellon died in 1999.

Mr. Beddall’s first wife, Priscilla Kimball Beddall, died in 1992 after 35 years of marriage.

Survivors include his wife of 19 years, Catherine Christine Larmore of Paris, Va.; four children from his first marriage, Laurence Beddall of New York, Frederic Beddall of Amherst, Mass., Margaret Beddall of Washington and Katherine Beddall of Vienna; and five grandchildren.