A World No. 1 player for a number of years, Jack Kramer is a possible candidate for the title of the greatest tennis player of all time. He was also, for many years, the leading promoter of the professional tennis tours and a relentless advocate for the establishment of Open tennis between amateur and professional players. Tall and slim, he was the first world-class player to play a consistent serve-and-volley game, in which he came to the net behind all of his serves, including the second serve. He was particularly known for his powerful serve and forehand, as well as his ability to play "percentage tennis", in which he maximized his efforts on certain points and certain games during the course of a match.

Within a year he was playing junior tournaments and taking lessons from a leading professional, Dick Skeen. Because of his obvious ability, in spite of his family's lack of money he had also come under the guidance of Perry T. Jones, the leading member of the Los Angeles Tennis Club and of the Southern California Association, the centers of American tennis in the 1930s. Kramer commuted many hours each day from his new home in Montebello to play at the LATC and the Beverly Hills Tennis Club, sometimes with such great adult players as Vines and Bill Tilden. He was the national boys' champion in 1936 and the winner of the 1938 Interscholastics. He was also competing occasionally in men's tournaments on grass courts in the East and winning matches against nationally ranked men such as Elwood Cooke.

In his 1979 autobiography, Kramer calls Helen Wills Moody the best women's tennis player he ever saw. He writes that when he was "the national boys' champion, fifteen years old," he played a match against her. "She was the champion of the world at the time -- she won seven Forest Hills and eight Wimbledons.... I beat her, but Helen played a good game."

Kramer attended Rollins College in Winter Park, Florida, and played on the tennis team there for at least the 1941 and 1942 seasons.

Kramer was inducted into the International Tennis Hall of Fame in Newport, Rhode Island, in 1968.