Chief among Lenglen's lawn-tennis titles were the Wimbledon singles (1919–23, 1925), women's doubles (1919–23, 1925), and mixed doubles (1920, 1922, 1925) as well as the French Open singles (1920–23, 1925–26), women's doubles (1925–26), and mixed doubles (1925–26). At the 1920 Olympic Games in Antwerp, Belgium, she earned gold medals in singles and mixed doubles. In world hard-court championship play she won the singles four times (1914, 1921–23), the women's doubles three times (1914, 1921–22), and the mixed doubles three times (1921–23). Her career was interrupted twice, first by World War I and later (1924) by illness.

In amateur lawn tennis Lenglen lost only one match: to Molla Bjurstedt Mallory (Mallory, Molla) at the 1921 U.S. Open in Forest Hills, New York. At Cannes, France, in 1926, she defeated the great American player Helen Wills (Wills, Helen) 6–3 and 8–6 in their only meeting, a widely publicized match. Later that year she traveled to the United States to join a professional tennis tour.

Although admired for her athleticism, Lenglen was equally renowned for her daring fashion choices. While most players preferred the traditional costume of a corset, hat, blouse, and long skirt, Lenglen's athletic wardrobe consisted of perfectly coordinated short pleated skirts, sleeveless blouses, and short-sleeved calf-length dresses worn without a petticoat. She often wrapped her head in a bandeau fastened with a jeweled pin. Her glamorous image was adored by fans and even led to the creation of the Lenglen tennis shoe.