By virtue of his long and prolific career, Connors still holds three prominent Open Era men's singles records: 109 titles (the only man to reach 100), 1535 matches played, and 1256 match wins. His titles include eight majors (five US Open, two Wimbledon, one Australian Open), three year-end championships, and 17 Grand Prix Super Series. In 1974, he became the second man in the Open Era to win three majors in a calendar year, and his total career match win rate remains in the top five of the era.

Connors continued to compete against younger men well into his 41st year.

Connors grew up in East St. Louis, Illinois, across the Mississippi River from St. Louis, and was raised Catholic. During his childhood he was coached and trained by his mother and grandmother. He played in his first U.S. Championship, the U.S. boys' 11-and-under of 1961, when he was nine years old. Connors' mother, Gloria, took him to Southern California to be coached by Pancho Segura, starting at age 16, in 1968. He and his brother, John "Johnny" Connors, attended St. Phillip's grade school.

In the open era, Connors is one of only six men to win three or more Grand Slam singles titles in a calendar year. The others are: Rod Laver who won the Grand Slam in 1969; Mats Wilander won the Australian, French and US Open in 1988; Roger Federer won the Australian, Wimbledon and US Open in 2004, 2006 and 2007; Rafael Nadal won the French, Wimbledon, and US Open in 2010; and Novak Djokovic won the Australian, Wimbledon, and US Open in 2011 and 2015.

Connors had shining moments against John McEnroe and Ivan Lendl, both of whom rose to prominence after Connors peaked in the mid-1970s. He would continue to compete against much younger players and had one of the most remarkable comebacks for any athlete when he reached the semifinals of the 1991 US Open at the age of 39.

He turned professional in 1972 and won his first tournament, the Jacksonville Open. Connors was acquiring a reputation as a maverick in 1972 when he refused to join the newly formed Association of Tennis Professionals (ATP), the union that was embraced by most male professional players, in order to play in and dominate a series of smaller tournaments organized by Bill Riordan, his manager. However, Connors played in other tournaments and won the 1973 U.S. Pro Singles, his first significant title, toppling Arthur Ashe in a five-set final, 6–3, 4–6, 6–4, 3–6, 6–2.

Connors won a male record 109 singles titles. He also won 15 doubles titles (including the men's doubles titles at Wimbledon in 1973 and the US Open in 1975).

Connors was engaged to fellow tennis pro Chris Evert from 1974-1975, and they each triumphed in the singles events at the 1974 Wimbledon Championships; a feat labelled "The Lovebird Double" by the media. Their engagement was broken off shortly before the 1975 Wimbledon championship. Connors and Evert briefly reconciled in 1976 and 1978, before parting for good. In May 2013, Connors wrote his autobiography in which he alleged that Evert was pregnant with their child and that she unilaterally made the decision to have it aborted.

Connors was taught to hit the ball on the rise by his teaching-pro mother, Gloria Connors, a technique he used to defeat the opposition in the early years of his career. Gloria sent her son to Southern California to work with Pancho Segura at the age of 16. Segura advanced Connors' game of hitting the ball on the rise which enabled Connors to reflect the power and velocity of his opponents back at them. Segura was the master strategist in developing Jimmy's complete game. In the 1975 Wimbledon final, Arthur Ashe countered this strategy by taking the pace off the ball, giving Connors only soft Jun K shots (dinks, drop shots, and lobs) to hit.

Former Miss World Marjorie Wallace was engaged to Connors from 1976-1977, but in 1979 Connors married Playboy model Patti McGuire. They have two children, son Brett and daughter Aubrey, and live in the Santa Barbara, California area.

At Wimbledon in 1977, he refused to participate in a parade of former champions to celebrate the tournament's centenary, choosing instead to practice in the grounds with Ilie Nastase while the parade took place. In 2000 he also declined to join a gathering of 58 former champions held to mark the millennium. In his 2013 autobiography Connors blamed his missing the 1977 parade on the All England Club for not letting his Doctor onto the grounds so that Connors could try on a customized splint for a thumb injury. Connors explained that this necessitated his rushing to meet the Doctor at the entrance to the grounds, and then convincing Nastase to help him try out the splint on a practice court. By Connors' account, he then rushed to Centre Court for the parade, but was too late. He was booed when he played his first round match the next day. Reaching the final, he lost in five sets to Borg, who a month later was able briefly to interrupt Connors's long hold on the world No. 1 ranking. Connors also irritated sponsors and tennis officials by shunning the end-of-year Masters championship from 1974 through 1976. However, he entered this round-robin competition in 1977 when it moved to New York City. Although Connors lost a celebrated late-night match to Vilas, 4–6, 6–3, 5–7, he took the title by defeating Borg in the final, 6–4, 1–6, 6–4.

In 1978, Borg defeated Connors in the Wimbledon final, but Connors defeated Borg at the US Open plus won the U.S. Pro Indoor. While he retained the ATP number ranking at the end of the year, the ATP and most tennis authorities rated Borg as the player of the year.

In his 1979 autobiography, tennis promoter and Grand Slam winning player Jack Kramer ranked Connors as one of the 21 best players of all time.

In the 1980 WCT Finals, Connors defeated the defending champion, John McEnroe. McEnroe and Borg were battling for the top spot in that year, while Connors played the role of the spoiler. However, in 1982, at age 29, Connors was back in the Wimbledon singles final, where he faced McEnroe, who by then was established firmly as the world's top player. Connors recovered from being three points away from defeat in a fourth-set tie-break (at 3–4) to win the match, 3–6, 6–3, 6–7, 7–6, 6–4, and claimed his second Wimbledon title, eight years after his first. Although Connors' tour record against McEnroe is 14–20, McEnroe is six years younger than Connors and had a losing record against Connors until he won 12 out of their last 14 meetings. Head to head in major championship finals, they split their two meetings, Connors winning the 1982 Wimbledon and McEnroe winning the 1984 Wimbledon.

Connors defeated another of the next generation of tennis stars, Ivan Lendl, in the 1982 US Open final and soon regained the world No. 1 ranking. Connors has a tour record of 13–22 against Lendl, but Lendl is seven years younger than Connors and had a losing record against Connors until he won their last seventeen matches from 1984 through 1992, after Connors' prime. Head to head in major championship finals, Connors took both meetings, winning the 1982 and 1983 US Open.

At the Tokyo Indoor in October 1983 Connors switched to a new mid-size graphite racket, the Wilson ProStaff, that had been designed especially for him and he used it on the 1984 tour. But 1985 again found Connors playing with the T2000. In 1987 he finally switched to a graphite racket when he signed a contract with Slazenger to play their Panther Pro Ceramic. In 1990 Connors signed with Estusa.

In the fourth round of the 1987 Wimbledon Championships, Connors defeated Mikael Pernfors, ten years his junior, 1–6, 1–6, 7–5, 6–4, 6–2, after having trailed 4–1 in the third set and 3–0 in the fourth set. In July 1988, Connors ended a four-year title drought by winning the Sovran Bank Tennis Classic in Washington, D.C. It was the 106th title of his career. Connors had played in 56 tournaments and 12 finals since his previous victory in the Tokyo Indoors against Lendl in October 1984.

In the fall of 1988, Connors auditioned to host the NBC daytime version of Wheel of Fortune, a show he and his wife "never missed an episode" of. However, the job went to Rolf Benirschke. According to show creator Merv Griffin, many news outlets tried to get their hands on Connors' audition tape, but Griffin refused to release it because he said "it wouldn't have been fair to Jimmy".

At the 1989 US Open, Connors defeated the third seed (and Future two-time champion), Stefan Edberg, in straight sets in the fourth round and pushed sixth-seeded Andre Agassi to five sets in a quarterfinal.

In the 1990s, he joined his brother John as Investors in the Argosy Gaming Company which owned riverboat casinos on the Mississippi River. The two owned 19 percent of the company which was headquartered in the St. Louis metropolitan area of East Alton, Illinois. Argosy narrowly averted bankruptcy in the late 1990s and Connors' brother John personally sought Chapter 7 bankruptcy. In the liquidation, Connors, through his company, Smooth Swing, acquired the Alystra Casino in Henderson, Nevada, for $1.9 million from Union Planters Bank, which had foreclosed on John. John had opened the casino in 1995 with announced plans to include a Jimmy Connors theme area. It was shuttered in 1998 and became a magnet for homeless and thieves who stripped its copper piping. The casino never reopened under Connors' ownership and it was destroyed in a May 2008 fire.

Connors recuperated and made an improbable run to the 1991 US Open semifinals which he later said were "the best 11 days of my tennis career." On his 39th birthday he defeated 24-year-old Aaron Krickstein, 3–6, 7–6, 1–6, 6–3, 7–6, in 4 hours and 41 minutes, coming back from a 2–5 deficit in the final set. Connors then defeated Paul Haarhuis in the quarterfinals before losing to Jim Courier. 22 years later ESPN aired a documentary commemorating Connors' run.

In September 1992, Connors played Martina Navratilova in the third Battle of the Sexes tennis match at Caesars Palace in Las Vegas, Nevada. Connors was allowed only one serve per point and Navratilova was allowed to hit into half the doubles court. Connors won, 7–5, 6–2.

However, this would not be the end of his playing career. As late as June 1995, three months shy of his 43rd birthday Connors beat Sébastien Lareau, 6–4, 7–6, and Martin Sinner, 7–6, 6–0, to progress to the quarterfinals of the Halle event in Germany. Connors lost this quarterfinal, 6–7, 3–6 to Marc Rosset. Connors' last match on the main ATP tour came in April 1996, when he lost, 2–6, 6–3, 1–6, to Richey Reneberg in Atlanta.

Connors was inducted into the International Tennis Hall of Fame in 1998 and Intercollegiate Tennis Association (ITA) Hall of Fame in 1986. He also has a star on the St. Louis Walk of Fame.

At a time when most other tennis pros played with wooden rackets, Connors used the "Wilson T2000" steel racket, which utilized a method for stringing that had been devised and patented by Lacoste in 1953. He played with this chrome tubular steel racket until 1984, when most other pros had shifted to new racket technologies, materials, and designs.

In October 2005, Connors had successful hip-replacement surgery at Cedars-Sinai Medical Center in Los Angeles.

On July 24, 2006, at the start of the Countrywide Classic tournament in Los Angeles, American tennis player Andy Roddick announced his partnership with Connors as his coach. On March 6, 2008, Roddick announced the end of that 19-month relationship.

On January 8, 2007, Connors' mother Gloria died at age 82.

On November 21, 2008, Connors was arrested outside an NCAA basketball game between the University of North Carolina at Chapel Hill and the University of California at Santa Barbara after refusing to comply with an order to leave an area near the entrance to the stadium. The charges were dismissed by a judge on February 10, 2009.

In Grand Slam Singles events, Connors reached the semifinals or better a total of 31 times and the quarterfinals or better a total of 41 times, despite entering the Australian Open Men's Singles only twice and not entering the French Open Men's Singles for five of his peak career years. The 31 semifinals stood as a record until surpassed by Roger Federer at Wimbledon 2012. The 41 quarterfinals remained an all-time record until Roger Federer surpassed it at Wimbledon 2014.

In 2013, Connors published his autobiography The Outsider. It won the British Sports Book Awards in the "Best Autobiography/Biography" category.

His on-court antics, designed to get the crowd involved, both helped and hurt his play. Schwartz said, "While tennis fans enjoyed Connors' gritty style and his never-say-die attitude, they often were shocked by his antics. His sometimes vulgar on-court behavior—like giving the finger to a linesman after disagreeing with a call or strutting about the court with the tennis racket handle between his legs; sometimes he would yank on the handle in a grotesque manner and his fans would go wild or groan in disapproval—did not help his approval rating. During the early part of his career, Connors frequently argued with umpires, linesmen, the players union, Davis Cup officials and other players. He was even booed at Wimbledon—a rare show of disapproval there—for snubbing the Parade of Champions on the first day of the Centenary in 1977." His brash behavior both on and off the court earned him a reputation as the brat of the tennis world. Tennis commentator Bud Collins nicknamed Connors the "Brash Basher of Belleville" after the St Louis suburb where he grew up. But Connors himself thrived on the Energy of the crowd, positive or negative, and manipulated and exploited it to his advantage in many of the greatest matches of his career.