Gardner J. O'Boyle, 84, a retired patent attorney and assistant professor of mathematics at Catholic University, died of pneumonia Saturday at Providence Hospital.

He had entered the practice of patent law in Washington in 1928 and was with the firm of Brady, O'Boyle and Gates when he retired in 1974.

Mr. O'Boyle had taught in the school of engineering and architecture at Catholic University from the early 1920s until retiring there in 1964.

He was born in Carbondale, Pa. After serving in France with the U.S. Army Signal Corps in World War I, he came here to attend Catholic University, where he earned bachelor's and master's degrees. He graduated from Georgetown University Law School in 1926.

During World War II, Mr. O'Boyle was a consultant to the Navy's Bureau of Yards and Docks and Bureau of Ships.

In 1962, he received an award from the Senators Club alumni group at Catholic University. The university presented him with a papal medal, Bene Merinti, a year later.

He is survived by his wife, Justine, of the home in Chevy Chase, D.C.; a son, James G., also of Chevy Chase, D.C.; four daughters, Jane O'Boyle, of the home, Justine Vieth and Janet Zambon, both of Kensington, and Sister Justine Marie, C.S.C, of Notre Dame, Ind., 13 grandchildren and three great-grandchildren.