During his career, he won eight Grand Slam singles titles and two Grand Slam doubles titles. He is generally considered to be one of the top male tennis players of all time.
Connors went to college for a year at UCLA, where he won the NCAA singles title in 1971. He turned professional in 1972, and won his first professional title later that year at Jacksonville, Florida.
Connors' extreme competitiveness on court quickly made him stand out. He simply refused to ever accept that he was beaten and gave absolutely everything on every point of every game, no matter how apparently hopeless the cause. He was also not averse to playing to the crowd or abusing his opponent or the umpire—anything he could think of to give himself an edge. His brash behaviour both on and off court came to earn him a reputation as the brat of the tennis world. He acquired the nickname of the "Brash Basher of Belleville" (after the St Louis suburb where he grew up). His high-profile romance with fellow teen tennis prodigy Chris Evert in the early years of his career also helped to keep him in the headlines.
Connors also acquired a reputation as a maverick in 1972 when he refused to join the newly formed Association of Tennis Professionals (ATP), the union which was embraced by most male professional players. He avoided the mainstream of professional tennis to play in, and dominate, a series of smaller tournaments organized by Bill Riordan, his manager and a clever promoter.
In 1974, Connors and Riordan began bringing lawsuits, eventually amounting to US$10 million, against the ATP and its President Arthur Ashe for allegedly restricting his freedom in the game. It started when Connors was banned from the French Open in 1974 after he had signed a contract to play World Team Tennis (WTT) for Baltimore (the ATP and the French administration opposed WTT because it conflicted with their tournament, and the entries of all WTT players were refused).
As it turned out, the French Open was the only major tournament which Connors did not win that year and his exclusion possibly prevented him from becoming the first male player since Rod Laver to win all four Grand Slam titles in one year. Though he would progress as far as the semifinals on four occasions, Connors would never prevail at the French Open. However, in 1974, Connors won the Australian Open, defeating Phil Dent in four sets in the final. Connors then beat Ken Rosewall in straight sets in the finals of both Wimbledon and the US Open. He won a total of 14 tournaments that year.
Connors reached the World No. 1 ranking in July 1974, and held it for 159 straight weeks. Over the course of his career, he held the World No. 1 ranking for a total of 263 weeks.
1975 saw Connors finish runner-up in the three Grand Slams he had won the year before. The 1975 Wimbledon final proved to be a duel between lawsuit opponents, as Connors faced ATP President Arthur Ashe. Ashe won, and shortly thereafter Connors dropped the suits and parted with Riordan.
In 1976, Connors met Björn Borg in the final of the US Open and saved four set points in a thrilling third-set tie-breaker (which Connors won 11–9) to beat the Swede 6–4, 3–6, 7–6, 6–4.
Despite his success, Connors remained an independent character with little respect for traditions and other people's expectations. At Wimbledon in 1977, he refused to take part in a parade of former champions to celebrate the tournament's centenary, and was booed when he went out to play the following day. He still managed to make the final at Wimbledon that year, but lost to Borg in a thrilling five-set final. He also lost in the final of the US Open to Guillermo Vilas. Having irritated sponsors and tennis officials by shunning the end-of-year Masters championships for the previous three years, Connors entered the competition for the first time in 1977 and beat Borg in the final to win the event.
Borg beat Connors comfortably in the 1978 Wimbledon final, but Connors came back and stunned the Swede in straight sets in the US Open final to win 6–4, 6–2, 6–2 in the first final to be held at the new Flushing Meadows venue.
With this US Open win, Jimmy Connors became the first (and only) tennis player to win this tournament on three different surfaces: Grass (1974), Clay (1976), and Hard Court (1978).
After a few less successful years on the tour, Connors was back in the Wimbledon final again in 1982 where he faced the new young star of the tennis world, John McEnroe. And Connors stunned the defending-champion as he came back from being three points away from defeat in a fourth-set tie-breaker to win in five sets and claim his second Wimbledon title eight years after his first.
Connors also got the better of another of the next generation of tennis stars, Ivan Lendl, in the US Open final in both 1982 and 1983.
Connors last Grand Slam final came at Wimbledon in 1984, where he again faced McEnroe. This time McEnroe put in a superlative performance and blew Connors off the court in straight sets 6–1, 6–1, 6–2. Though beaten, Connors' competitive fire was certainly not dampened. Asked afterwards if he now admitted his rival was the better player, he simply replied: "Never".
Considered a feisty wiseguy in his earlier days, Connors gradually transformed himself into a respected elder of the tennis world in the later years of his career. He continued to compete forcefully against much younger men until he was well into his 41st year.
The defining moment of Connors' later career came in 1991. His career had seemed to be at an end in 1990, when he played only three tournament matches (and lost all three), dropping to No. 936 in the world rankings. But after surgery on his deteriorating left wrist, he came back to play 14 tournaments in 1991, climaxing with a phenomenal run at the US Open. While celebrating his 39th birthday during the championships, Connors powered his way all the way through to the semi-final before finally being beaten by the reigning French Open champion Jim Courier.
During his career, Connors won a record 109 men's singles titles. He also won 15 doubles titles (including the men's doubles titles at Wimbledon in 1973 and the US Open in 1975).
In his 1979 autobiography, Jack Kramer, the long-time tennis promoter and great player himself, ranks Connors as one of the 21 best players of all time. Connors was inducted into the International Tennis Hall of Fame in Newport, Rhode Island in 1998 and has his own star on the St. Louis Walk of Fame.