Kobashi practiced judo and rugby union during high school in Fukuchiyama. He practised body building after his graduation while working "regular" jobs. He applied and was accepted to All Japan Pro Wrestling's dojo on June 20, 1987. He was trained there by Dory Funk, Jr., Giant Baba, Kazuharu Sonoda and Masanobu Fuchi. Kobashi debuted as a professional wrestler in Ryuo, Shiga on February 26, 1988. He was booked by Shohei "Giant" Baba to lose his first 63 matches (all singles bouts). It was all part of Baba's master plan: even in defeat, the fiery, charismatic Kobashi shined, and his gutsy, never-say-die efforts earned him the Rookie of the Year award from the Japanese press. Kobashi won his first match in May 1989 (against Jim Crockett Promotions jobber Mitch Snow). During 1989, when the Road Warriors were in AJPW, they taught Kobashi the "Road Warrior Workout". He first gained some prominence as member of Mitsuharu Misawa's faction during Misawa's feud with Jumbo Tsuruta.

In 1993, he became Misawa's main tag partner in the middle of the year when Kawada became Misawa's main rival. He gained his first singles victory over a former Triple Crown Heavyweight Champion, when he defeated Terry Gordy in May of that year. On December 3, 1993 Kobashi gained his first pin over Kawada, won his first World's Strongest Tag Determination League, and won his first World Tag Team Championship. Kobashi received his first shot at the Triple Crown Championship against then-champion Steve Williams on September 3, 1994, but lost at Nippon Budokan, Tokyo. Kobashi's singles matches around this time with Kawada, Misawa and Stan Hansen are amongst his most highly regarded. In tag competition he had strong efforts with opponents as diverse as rookie Jun Akiyama to elderly legend and promotion owner Giant Baba. Over the next few years Kobashi continued to gain more honors, but his position in the company did not truly change. In the 1994 Champion Carnival he gained his first singles victory over Hansen. In September 1994 he lost his first Triple Crown challenge against Steve Williams. His next title challenge was against Kawada in January 1995. This led to a 60-minute time limit draw, and is regarded as the greatest 60 minute bout in wrestling history by the Wrestling Observer Newsletter. On June 9, 1995, Kobashi and Misawa lost the tag title to Akira Taue and Toshiaki Kawada. The match is also notable because it won the best match of the year award from Tokyo Sports. He suffered the first of many knee injuries in mid 1995, but worked through it. In the early part of 1996 the company elevated Jun Akiyama by making him Misawa's main tag partner. While this was good for Akiyama and lead to some fresh tag matches, it left Kobashi without a real tag partner for most of the year.

Kobashi defeated Akira Taue on July 24, 1996 to capture his first Triple Crown. He lost the championship to Misawa on January 20, 1997, in a very highly regarded match. In March 1997 in the Champion Carnival he gained his first pinfall victory over Misawa. At the end of the Carnival, Kobashi qualified for the finals for the first time. However, instead of the traditional one on one contest to settle the carnival, a one night 3 way round robin was held due to Kobashi, Kawada, and Misawa all having finished the Carnival round robin with the same score. In the first match Kobashi went to a 30 minute draw with Misawa. However, this match left both men greatly weakened and Kawada was able to quickly gain his first singles pin over Misawa in the next match that gave Kobashi little time to rest. In the final match Kawada defeated Kobashi to gain his second Carnival title. In October 1997 Kobashi won his first tag title without Misawa when he and Johnny Ace defeated Gary Albright and Steve Williams. In the same month he challenged Misawa for the Triple Crown in another memorable match, but again Misawa defeated him. While Kawada would finally end his quest to defeat Misawa for the Triple Crown at AJPW's May Tokyo Dome show, in 1998, Kobashi would replace Kawada as Misawa's top rival. On June 12, 1998 Kobashi defeated Kawada to begin his second Triple Crown reign. Shortly before his victory he again suffered a major knee injury which he would not give time to heal, which nearly ended his career. He lost the championship again to Misawa.

1998 would end with Kobashi gaining another career milestone as he with Akiyama, teaming as "Burning", captured his first World's Strongest Tag Determination League championship. As January began Kobashi was kicking off a new rivalry against Vader. He won the World's Strongest Tag Determination League again with Akiyama in December 1999. In February 2000 he defeated Vader to earn his third Triple Crown reign. Then in April 2000 he won his first Champion Carnival while in the course of the tournament gaining his first televised singles victory over Misawa. In mid-2000 Misawa left the company to form Pro Wrestling Noah; Kobashi, along with all but three All Japan native workers, followed Misawa. He was the reigning Triple Crown champion at the time, and the championship was thus vacated. Despite Kobashi's injuries, it was at around this time that many Japanese wrestling magazines began calling Kobashi "the perfect wrestler," standing at an impressive 6-2 and 280 lbs., Kobashi possessed the strength to out-power most wrestlers, yet he was also able to perform a moonsault with the skill of a lightweight.

During this period Kobashi's knee injuries were beginning to worsen to the point that he desperately needed time off to heal. However, he was needed to establish Noah as a viable promotion, and was given a marquee position on the first two shows. On August 5, 2000, he teamed with Akiyama to defeat Misawa and Taue in a two out of three falls match in the main event of the promotion's first show, and then lost to Akiyama on the second show the next day (Kobashi legitimately passed out while being captured in Akiyama's "King Crab Lock" submission and was unable to finish the match). Noah struggled to organize itself without any titles during this period. At the biggest Noah show of the year on December 23, 2000 Kobashi defeated Akiyama, avenging his loss earlier that year. Unfortunately for Kobashi the next month his knees finally deteriorated to the point he could no longer work through the pain and he was forced to take 13 months off for healing. He went through multiple knee surgeries during this time.[2]

His return match was on February 24, 2002, and featured Kobashi reforming his pairing with Misawa to face Akiyama and New Japan Pro Wrestling's Yuji Nagata. His knees again gave out on him during the match. After taking another 5 months to recuperate he returned and Noah began to slowly build towards him winning their top prize, the GHC Heavyweight Championship.

On March 1, 2003 Kobashi defeated his rival Mitsuharu Misawa in a match for the GHC Heavyweight Championship. Kobashi's reign spanned for over two years and included 13 successful defenses. Notable defences included: against Masahiro Chono at New Japan's May 2, 2003 Tokyo Dome event, against Yuji Nagata on September 12, 2003, against Yoshihiro Takayama on April 25, 2004, and against Jun Akiyama in the main event of Noah's first Tokyo Dome show on July 10, 2004. During his reign he won the Wrestling Observer Newsletter's Wrestler of the Year award in both 2003 and 2004. In March 2005 he finally lost the championship to Takeshi Rikio. Despite the loss of his title Kobashi remained Noah's top wrestler, the rest of the year was highlighted by matches with outsiders such as Genichiro Tenryu and Kensuke Sasaki (the latter on July 18, 2005 in the Tokyo Dome), and in the following year he had praised matches against junior heavyweights such as Kenta (March 5, 2006) and Naomichi Marufuji (April 23, 2006). Kobashi holds the distinction of having competed in a total of 23 5-Star Matches as rated by Dave Meltzer of the Wrestling Observer, second only to his long-time rival, Misawa.

In late 2005, Kobashi made his first appearance in North America with Harley Race's World League Wrestling promotion, defeating then WLW champion Wild Wade Chism. His second and third North American appearances were for Ring of Honor, where he defeated Samoa Joe in a memorable singles match (given a full 5-stars by the Wrestling Observer as well as their Match of the Year award for 2005), and teamed with Homicide to defeat the tag team of Low Ki and Samoa Joe. Kobashi also traveled to Europe, where he had matches in Germany, and at Universal Uproar in England, in November 2005. After winning the GHC Tag Team Championship on June 4, 2006, Kobashi became inactive in the sport due to cancer, resulting in his partner Tamon Honda returning the belts on September 26, 2006. On December 10, at the Nippon Budokan, Kobashi appeared before the fans and announced that he would return "without fail".

On September 8, 2007, news broke that Kobashi would make his return on the December 2, 2007, Budokan Hall event where he would team up with Takayama to face Akiyama and Misawa. On the card, Misawa would pin Kobashi with an avalanche Emerald Flowsion, but the fans still gave Kobashi a rousing ovation.

Kenta Kobashi made his return to wrestling on March 1, 2009 at Nippon Budokan with Pro Wrestling Noah, defeated Masao Inoue in the opening match of the card with his signature lariat. Kobashi won the GHC Openweight Hardcore Championship from Makoto Hashi on June 8, 2009 in Hachiōji, Japan during Noah's Southern Navigation tour.

On December 23, 2009, Kobashi was seriously injured in a three-way match against Honda and Kikuchi. He was sidelined for 19 months with nerve damage in his right arm. Kobashi made his return on July 23, 2011, teaming with Go Shiozaki in a tag team match, where they were defeated by Akitoshi Saito and Jun Akiyama. On August 27, 2011, he debuted new ring gear, mixing black and orange, at the NJPW/AJPW/Noah All Together show at Budokan Hall, teaming up with AJPW's Keiji Mutoh, defeating NJPW's Takashi Iizuka and Toru Yano. On October 6, it was announced by Noah that Kobashi had stepped down from his position as an Executive Vice President of the promotion.[4] On December 3, 2012, Noah released Kobashi from his contract.[5] The news sparked shockwaves, as Atsushi Aoki, Go Shiozaki, Jun Akiyama, Kotaro Suzuki, and Yoshinobu Kanemaru spoke out, declaring their intent of not signing with Noah after their contracts expire in January, out of loyalty to Kobashi.[6][7]

On March 17, 2013, Kobashi made an appearance for All Japan Pro Wrestling to promote his retirement match. Before the main event, Hiroshi Hase announced that he would be resigning as Pacific Wrestling Federation (PWF) chairman to focus on the National Diet and that Kobashi would be replacing him, after his retirement on May 11.[13] He has yet to officially take on the new job. On September 8, Kobashi appeared as a color commentator at All Japan splinter promotion Wrestle-1's inaugural event.[14] On October 27, it was confirmed that Kobashi would not be joining All Japan after all, when Dory Funk, Jr. was announced as the new PWF chairman.[15]

On February 14, 2014, Kobashi announced that starting June 8, he would begin producing his own independent events under the brand "Fortune Dream".[16] The inaugural event featured wrestlers from various promotions, including All Japan Pro Wrestling, Big Japan Pro Wrestling, Kaientai Dojo, Pro Wrestling Zero1 and Wrestling New Classic.[17]

On March 1, 2003 Kobashi defeated his rival Mitsuharu Misawa in a match for the GHC Heavyweight Championship. Kobashi's reign spanned for over two years and included 13 successful defenses. Notable defences included: against Masahiro Chono at New Japan's May 2, 2003 Tokyo Dome event, against Yuji Nagata on September 12, 2003, against Yoshihiro Takayama on April 25, 2004, and against Jun Akiyama in the main event of Noah's first Tokyo Dome show on July 10, 2004. During his reign he won the Wrestling Observer Newsletter's Wrestler of the Year award in both 2003 and 2004. In March 2005 he finally lost the championship to Takeshi Rikio. Despite the loss of his title Kobashi remained Noah's top wrestler, the rest of the year was highlighted by matches with outsiders such as Genichiro Tenryu and Kensuke Sasaki (the latter on July 18, 2005 in the Tokyo Dome), and in the following year he had praised matches against junior heavyweights such as Kenta (March 5, 2006) and Naomichi Marufuji (April