In 1946 he went on his own to live in Ereven, Armenia. That year he won the Armenian championship. He repeated winning the Armenian championship in 1948. In 1949 Petrosian moved to Moscow and began winning more tournaments.

In 1951 he won the Moscow championship. In the 1951 USSR championship he took second place, behind Paul Keres.

At the Saltsjobaden interzonal in 1952, Petrosian took second place, behind Alexander Kotov, with 7 wins and 13 draws.

In 1953 Petrosian took 5th place in the powerful Neuhausen-Zurich Candidates tournament with 6 wins, 18 draws, and 4 loses. At the next interzonal, Gothenburg 1955, he came in fourth place with 5 wins and 15 draws.

In 1956 he shared third place in the Amsterdam Candidates tournament with 3 wins, 13 draws, and 2 losses. That year he also won the Moscow championship.

Petrosian shared 3rd place at the 1958 Portoroz interzonal and came 3rd in the following Candidates tournament. He took 2nd place in the 1958 USSR championship, behind Mikhail Tal.

In 1959 Petrosian won the USSR championship with 8 wins and 11 draws. In 1960 he took second in the USSR championship, behind Victor Korchnoi with 10 wins, 7 draws, and 2 losses.

In February, 1961 Petrosian won the 28th USSR championship in Moscow with 9 wins, 9 draws, and 1 loss.

At the Stockholm interzonal in 1962 Petrosian shared second place with 8 wins and 14 draws. He then took first place at the 1962 Curacao Candidates tournament (Fischer took 4th) to become the challenger for the world chess championship. In 1963 Petrosian challenged Mikhail Botvinnik for the world championship and won with 5 wins, 15 draws, and 2 losses.

From 1963 to 1966, Petrosian was the chief editor of the monthly Soviet chess magazine, SHAKHMATNAYA MOSKVA.

Petrosian tied for first place at the First Piatigorsky Cup in Los Angeles in 1963 with Paul Keres. He scored 4 wins, 9 draws, and 1 loss.

In 1964 Petrosian tied with Paul Keres at Buenos Aires, scoring 8 wins and 9 draws. In 1964 the first unofficial international rating list was published by Arpad Elo. The top two players, with a 2690 rating, were Tigran Petrosian and Bobby Fischer.

In 1966 Petrosian played Boris Spassky and succesfully defended his title, to remain world champion. Petrosian had won 4 games, drew 17, and lost 3. He received $2,000 for his efforts.

Petrosian won the Moscow championship for the third time in 1968 with 6 wins and 9 draws. In 1968 Petrosian recieved his Masters degree from Ereven University. His dissertation was entitled, 'Chess Logic.'

From 1968 to 1977, Petrosian was the chief editor of the weekly chess and checker magazine, 64.

In April 1969 Petrosian met Spassky again for the world championship, but lost the title with 4 wins, 13 draws, and 6 losses. In late 1969 Petrosian again won the USSR chess championship with 6 wins and 16 draws.

In 1971 Petrosian defeated Robert Huebner with 1 win and 6 draws in the quarter-finals Candidates match. He then defeated Victor Korchnoi with 1 win and 9 draws in the semi-finals match. He finally lost to Bobby Fischer in Buenos Aires. He had won 1 game, drawn 3 games, and lost 4 games. When Petrosian lost his match to Fischer, his wife put the blame on his trainer, Alexei Suetin, and slapped him.

In 1972 Petrosian tied for first place at the Church's Fried Chicken International Tournament in San Antonio, Texas with Anatoly Karpov and Lajos Portisch. At the 1972 Skopje Olympiad, Petrosian lost his one and only game on time to Robert Huebner. When he was later told that the incident had been shown on TV, he said, "If I had known that, I would definitely smashed the clock."

Petrosian tied for first place with Albin Planinc at Amsterdam 1973 and tied for first with Leonid Stein at Las Palmas.

In 1974 Petrosian defeated Lajos Portisch, but lost to Victor Korchnoi in the Candidates matches. He took 2nd place at Milan 1974.

Petrosian took 2nd at Manila 1975.

Between 1968 and 1975, Petrosian never lost more than a single game in any tournament he played in. At the Biel interzonal in 1976, Petrosian took second, behind Bent Larsen, with 6 wins, 12 draws, and 1 loss.

Tigran Petrosian and Vasily Smyslov were the first two Soviets to play in the Lone Pine tournaments. Petrosian won Lone Pine in 1976.

In 1977 Petrosian lost to Korchnoi in the quarter-final Candidates match. That match was played behind a bullet-proof screen.

In 1979 he took first at Tallinn with 8 wins and 8 draws. He then tied for first place with Huebner and Portisch at the 1979 Rio de Janeiro interzonal.

In 1980 Petrosian again lost to Korchnoi in the quarter-final Candidates match. Afterwards, he took first place at Las Palmas 1980. In ten chess Olympiads, Petrosian won prizes for the highest score six times, scoring 79 wins, 50 draws, and 1 loss.