Korchnoi is best known for playing three matches against Anatoly Karpov for the World Chess Championship. In 1974, he lost the Candidates final to Karpov, who went on to win the World championship by forfeit against Bobby Fischer. Then, after defecting from the Soviet Union in 1976, he won the Candidates twice to qualify for World Championship matches against Karpov in 1978 and 1981, losing both times.
In all, Korchnoi was a Candidate for the World Championship on ten occasions (1962, 1968, 1971, 1974, 1977, 1980, 1983, 1985, 1988 and 1991). Korchnoi is also a four-time USSR chess champion (1960, 1962, 1964–65, 1970), a five-time European champion, and a six-time member of Soviet teams that won the Chess Olympiad. In September 2006, he won the World Senior Chess Championship.
He learned to play chess from his father at the age of seven. In 1943, he joined the chess club of the Leningrad Pioneer Palace, and was trained by Abram Model, Andrei Batuyev, and Vladimir Zak. In 1947, he won the Junior Championship of the USSR, with 11.5/15 at Leningrad, and tied for that title again in 1948 with 5/7 at Tallinn. In 1951 he earned the Soviet Master title, following his second place in the 1950 Leningrad Championship, with 9/13.
Korchnoi's playing style initially was an aggressive counter-attack. He excelled in difficult defensive positions. His results during the 1950s were often inconsistent, as dominance alternated with disaster. One horrific result was his 19th place (only one from bottom) at the URSch-22, Moscow 1955, with just 6/19. During the 1960s he became more versatile, mastering all the required techniques to become a world championship contender. He won at Krakow 1959 with 8.5/11, shared 1st–2nd places with Samuel Reshevsky at Buenos Aires 1960 with 13/19, won at Córdoba, Argentina 1960 with 6/7. After his victory at Budapest 1961 (Géza Maróczy Memorial) with 11.5/15 ahead of Bronstein and Miroslav Filip each with 9.5, Korchnoi was recognized as one of the world's four best players along with Botvinnik, Tal, and Fischer.
Korchnoi won the USSR Chess Championship four times during his career. At Leningrad 1960 for URS-ch27, he scored 14/19. He won at Yerevan 1962, URS-ch30, with 13/19. He won at Kiev 1964–65 with 15/19. His final title was at Riga 1970, for URS-ch38, with 16/21.
He never succeeded in becoming World Champion, but many people consider him the strongest player never to have done so, a distinction also often attributed to Paul Keres. When Spassky beat Petrosian to claim the World Title in 1969, the Soviet Chess Federation started pursuing a youth policy which largely classed Korchnoi and Vasily Smyslov as the old vanguard; as a consequence, they were sometimes overlooked when it came to distribution of opportunities to play in international chess tournaments.
Korchnoi won at Havana 1963 with 16.5/21, but fared poorly in the next Soviet Championship, URS-ch31 at Leningrad, with just 10/19 for 10th place. He missed qualifying for the next world championship cycle, 1964–66, because of a relatively poor showing at the 1964 Zonal tournament in Moscow, where he made 5.5/12 for a shared 5–6th place, so did not advance to the Interzonal. Korchnoi regained his form with an overwhelming triumph at Gyula 1965 with 14.5/15. He won at Bucharest 1966 with 12.5/14, and at the Chigorin Memorial in Sochi 1966 with 11.5/15.
He tied for 3rd-5th places at the URS-ch34, Tbilisi 1966–67, with 12/20, and advanced from a playoff at Tallinn 1967 to the Sousse Interzonal later that year. A strong performance at the 1967 Sousse Interzonal, with 14/22, for a shared 2nd–4th place, took him through to the Candidates' matches. In his first match, he defeated American Samuel Reshevsky at Amsterdam 1968 by (+3 =5 -0). Next up was Mikhail Tal, against whom Korchnoi had had a big edge in previous games. The match, held in Moscow 1968, was close, but Korchnoi won by 5.5 to 4.5, and moved on to face Boris Spassky in the Candidates final. Spassky proved to be too much for him, at Kiev 1968, winning 6.5–3.5.
Korchnoi, as the losing finalist, was exempt from qualifying for the next cycle (1970–72), and advanced directly to the Candidates' matches. First, he played a training match against Anatoly Karpov, with whom he was close at the time, at Leningrad 1971; this wound up drawn in six games. Korchnoi won his first round 1971 match against Efim Geller at Moscow by 5.5–2.5, but then lost to Tigran Petrosian by 5.5–4.5, also at Moscow. Anatoly Karpov, in his book Karpov on Karpov (Atheneum 1993), writes that, because of Bobby Fischer's overwhelming form at that time, Korchnoi and Petrosian were asked by Soviet chess authorities to choose among themselves, before the match, who they thought would have the better chance of stopping Fischer in the finals. Petrosian apparently believed strongly in himself, and so Korchnoi was asked to throw the match, receiving as compensation invitations to the three most prestigious tournaments in western Europe. Petrosian, however, lost to Fischer by a one-sided score late in 1971.
Korchnoi's mood largely dictated his plan for the game. He was comfortable playing with and without the initiative. He could attack, counterattack, play positionally, and was a master of the endgame. He became known as the master of counter-attack, and strangely enough he was Mikhail Tal's (an out-and-out attacker) most difficult opponent. He has a large lifetime plus score against Tal, and also has plus scores against world champions Petrosian and Spassky. He has equal records against Botvinnik and Bobby Fischer. He has beaten the eight undisputed world champions from Botvinnik to Garry Kasparov, as well as FIDE world champions Ruslan Ponomariov and Veselin Topalov.
Korchnoi and Anatoly Karpov, the newest young star of the Soviet chess school, tied for first in the 1973 Leningrad Interzonal. In the 1974 Candidates' matches, Korchnoi first beat the young Brazilian star Henrique Costa Mecking (who had won the other Interzonal, in Petropolis) by 7.5–5.5 at Augusta – in what he later described as a tough match in his autobiography. Korchnoi next played former World Champion Tigran Petrosian at Odessa. The two were not on friendly terms, and it was even rumored that the two resorted to kicking each other under the table during this match. However, Korchnoi denies this. According to him, Petrosian just kicked his legs nervously and shook the table. Although the match was supposed to go to the first player to win four games, Petrosian resigned the match after just five games, with Korchnoi enjoying a lead of 3-1, with one draw.
With his victory over Petrosian, Korchnoi advanced to the Candidates' Final, the match to determine who would challenge reigning World Champion Bobby Fischer in 1975. Korchnoi's opponent was Karpov. In the run-up period before the match, Korchnoi was constantly subjected to threats and harassment, and was virtually unable to find any Grandmasters to assist him. David Bronstein apparently assisted Korchnoi somewhat, for which he was punished. Clearly, the Soviet chess hierarchy favoured the younger Karpov, reasoning that the generation which had been defeated by Fischer (of which Korchnoi was part), could not hope to battle him successfully. Korchnoi did receive some assistance later in the match from two strong British Masters, Raymond Keene and William Hartston. Korchnoi trailed 3-0 late in the match, but won games 17 and 21 to make it very close right to the end. Karpov eventually won this epic battle, played in late 1974 in Moscow, by a 12.5–11.5 score. By default, Karpov became the Twelfth World Champion in April 1975, when Fischer refused to defend his title because of disputed match conditions.
During the match between Karpov and Korchnoi, an amusing incident occurred. In the 21st game, Korchnoi played a strong opening novelty and, after a terrible blunder by Karpov, had achieved an overwhelming position. During this game, Korchnoi got up from the board, walked over to the arbiter and asked whether he could legally castle king-side in the current position, in which a bishop was attacking his rook on h1. The arbiter, Salo Flohr, informed him that he could. Korchnoi did so, and Karpov soon resigned.
Korchnoi, in a 2006 lecture in London, mentioned that the breakthrough that allowed him to resume international appearances came when Anatoly Karpov inherited the World Championship title (resigned by Bobby Fischer). Questions arose about how Karpov qualified to be a World Champion, when he had never played Fischer. Since Korchnoi was not publicly visible, it was largely believed that he (and Karpov) could not be very strong. Korchnoi was then allowed to play the 1976 Amsterdam tournament, as a means to prove Karpov was a worthy World Champion.
Korchnoi was joint winner of the tournament along with Tony Miles. At the end of the tournament, Korchnoi asked Miles to spell 'political asylum' for him. As a result, after the chess tournament in Amsterdam, Korchnoi was the first strong Soviet grandmaster to defect from the Soviet Union. Korchnoi's defection resulted in a turbulent period of excellent tournament results, losses in the two matches for the World Title – all overshadowed by the oppressive political climate of the Cold War.
Korchnoi resided in the Netherlands for some time, giving simultaneous exhibitions. He played a short match against Jan Timman – the strongest active non-Soviet player at that time – and comprehensively defeated him. He moved to West Germany, and then eventually settled in Switzerland by 1978.
The World Championship match of 1978 was held in Baguio in the Philippines, and deserves its reputation as the most bizarre World Championship match ever played. Karpov's team included a Dr. Zukhar (a well known hypnotist), while Korchnoi adopted two local renegades currently on bail for attempted murder. There was more controversy off the board, with histrionics ranging from X-raying of chairs, protests about the flags used on the board, the inevitable hypnotism complaints and the mirror glasses used by Korchnoi. When Karpov's team sent him a blueberry yogurt during a game without any request for one by Karpov, the Korchnoi team protested, claiming it could be some kind of code. They later said this was intended as a parody of earlier protests, but it was taken seriously at the time.
In quality of play the match itself never measured up to the press headlines that it generated, although as a sporting contest it had its share of excitement. The match would go to the first player to win six games, draws not counting. After 17 games, Karpov had an imposing 4–1 lead. Korchnoi won game 21, but Karpov won game 27, putting him on the brink of victory with a 5–2 lead. Korchnoi bravely fought back, scoring three wins and one draw in the next four games, to equalise the match at 5–5 after 31 games. However, Karpov won the very next game, and the match, by 6–5 with 21 draws.
Korchnoi took the opportunity of the match to publicize the situation of his wife and son, drafting an open letter to the Soviet government to release them both.
In what was dubbed the "Massacre in Merano", Karpov defeated Korchnoi convincingly by 6 wins to 2, with ten draws.
The match was to be held in Pasadena, California, but the Soviet Chess Federation protested (possibly because Korchnoi was a defector and the match was in the cold-war enemy's back yard, and because of the soon-to-be-announced Soviet decision to boycott the 1984 Olympic Games in Los Angeles), and Kasparov was not allowed to fly there to play the match. This defaulted the match to Korchnoi.
However, after a remarkable series of events, spearheaded by the British Grandmaster Raymond Keene, Korchnoi agreed to play the match in London. This was a gracious gesture by Korchnoi, since technically he had already won by default. After a good start, Korchnoi was blown away by Kasparov's attacking play and remarkable maturity.
After the 1983 Kasparov match, Korchnoi continued playing at a top level but without seriously threatening the world championship again. In the 1985–87 World Championship cycle he finished equal thirteenth out of 16 in the Candidates' Tournament. In the 1988–90 cycle he made the final 16 again, but was eliminated in the first round of Candidates' matches. In the 1991–93 cycle he reached the final 8 of the Candidates' before being eliminated.
He continues playing in Europe to this day, living in his adopted country of Switzerland, which he represents on the top board of the World Chess Olympiad, most recently playing in Torino, Italy, in 2006.
Korchnoi is noted for his unusual longevity at the chessboard. He has been at or near the top of the game for nearly half a century. He continues to play many tournaments every year, playing more than 15 tournaments in 2006. He won the 2005 Quebec Open in Montreal. In August 2006 at age 75 he won the Banyoles Open in Spain ahead of Sergei Tiviakov.
On the January 2007 FIDE rating list Korchnoi was ranked number 85 in the world at age 75, by far the oldest player ever to be ranked in the FIDE top 100. The second-oldest player on the January 2007 list was Alexander Beliavsky, age 53, who is 22 years younger than Korchnoi.