On June 16, 1886, "shy" Clara Cook married Frank B. Kellogg, the thirty-year-old attorney for Olmsted County, Minnesota. Frank Kellogg soon moved on to earn a fortune in private practice in St. Paul and later entered public life as a United States senator, ambassador to Great Britain, and secretary of state. His wife established a reputation as a popular hostess in Washington and London. "She was a tactful, patient woman," noted Time magazine upon her death at the age of eighty, "whose grace often counteracted her husband's impulsive conversation." President Calvin Coolidge, Frank Kellogg reported, said he had made him ambassador "as much because of Mrs. Kellogg as for himself."
Clara Kellogg posed for Philip de Lászlo-famous as a society painter, especially of beautiful women-at London in April 1929 for a picture commissioned as a pendant to the artist's second portrait of her husband.