Sears was the daughter of Boston businessman Frederick Richard Sears, a cousin of Henry Cabot Lodge, and a great-granddaughter of Thomas Jefferson.
She won the women’s doubles at the US Women’s National Championship four times, including three consecutively (1915–1917). In singles, she was a finalist in 1912, where she was beaten in straight sets by Mary Kendall Browne.
She was inducted into the International Tennis Hall of Fame in 1968, joining her cousin Richard (inducted 1955).
Eleonora Sears rode horses competitively and was elected to the US Show Jumping Hall of Fame in 1992. She also owned and raced Thoroughbred horses. She was the first woman to play polo on a men’s team.
Sears was the first female national squash champion, a founder of the Women’s Squash Racquets Association, and coach of the U.S. Women’s International Squash Team.
She gained media attention for her long distance walks and hikes. As well, she was one of the first American women to drive an automobile and fly a plane.
Her habit of wearing trousers, both when competing in sports and in public, was criticized in media and social circles.