Moore usually found himself in trouble as a youngster, and he was in a reformatory until 1934. In 1935, he began his amateur career, and had nine fights as an amateur, winning 5 and losing 4. But he claimed that he boxed some fights under the name of Fourth of July Kid, therefore, he might have had more fights as an amateur.
He began his professional career in 1936, with a six round win over Murray Allen. After a draw with Speedy Schaeffer, he and Allen met again, and this time Moore won by a knockout in 2. In 1937, he won nine bouts in a row by knockout until he suffered his first defeat, an eight round decision loss to Billy Adams. Some historians say that fight actually took place in 1936, but officially it took place in 1937. He then won seven straight fights, six by knockout, before losing again, to Johnny Bandit Romero by a decision in ten in San Diego in 1938. He boxed all but one of his 12 bouts in San Diego that year. In a rematch with Romero, he won by a knockout in four.
Moore had eight bouts in 1939, going 5-2 during that span, with one no contest. He lost to fringe contender Teddy Yarosz during that time, and his no contest was against Jack Coggins, in eight rounds. In 1940, Moore went on a tour of Australia, fighting in Melbourne, Tasmania, Adelaide and Sydney. He won all of his seven bouts there, including six by knockout. Upon returning to the United States, he defeated Pancho Ramirez by a knockout in five, but lost to Shorty Hogue on a six round decision.
Moore had four fights in 1941, period during which he went 2-1-1, and he drew with Eddie Booker. By then, however, he had suffered several stomach ulsers, with their resulting operations. So he announced his retirement from boxing.
His retirement lasted a short period of time however, and in 1942, he was back in the ring. He won his first six bouts that year, including a second round knockout over Hogue in a rematch, and a ten round decision over Jack Chase. Then, he met Booker in a rematch, and they had the same result as in their previous meeting: another 10 round draw.
In 1943, Moore had seven bouts, winning 5 and losing two. He won and lost the California State Middleweight title against Chase, both by 15 round decisions, and beat Chase again in his last bout of that year, by a ten round decision. He also lost a decision to Aaron Wade that year.
In 1944, he had nine bouts, going 7-2. His last bout marked his debut on the Atlantic Coast. That year, his opposition level began to improve, and he beat Jimmy Hayden by a knockout in five, lost to Charlie Burley by a decision, and to Booker by a knockout in eight.
He won his first eight bouts of 1945, impressing Atlantic coast boxing experts, and earning a fight with fringe contender Jimmy Bivins, who defeated Moore by a knockout in six at Cleveland. He returned to the Eastern Seaboard, and fought five more times before that year was over. He met, among others, Holman Williams during that span, losing a ten round decision, and knocking him out in eleven in the rematch.
By 1946, Moore had moved to the Light Heavyweight division, and he went 5-2-1 that year, beating fringe contender Curtis Sheppard, but losing to future world Heavyweight champion Ezzard Charles by a decision in ten, and drawing with old nemesis Chase. By then, Moore began complaining that, according to him, none of boxing's world champions would risk their titles against him.
1947 was basically a year of rematches for Moore. He went 7-1 that year, his lone loss being to Charles. He beat Chase by a knockout in nine, Sheppard by a decision in ten and Bivins by a knockout in nine. He also defeated Bert Lydell, by a decision in ten.
He had 14 fights in 1948, losing again to Charles by a knockout in nine, losing to Bivins by a knockout in the first, to Henry Hall by a decision in ten and to Lloyd Gibson by a disqualification in four. But he also beat Ted Lowry, by a decision in ten, and Hall in a rematch, also by decision.
1949 was a good year for The Ol' Mongoose: He had 13 bouts that year, going 12-1. He defeated Alabama Kid twice; by knockout in four and by knockout in three, Bob Satterfeld by a knockout in three, Bivins by a knockout in eight, future world Light Heavyweight champion Harold Johnson by a decision, Bob Sikes by a knockout in three, and Phil Muscato by a decision. He lost to Clinton Bacon by a disqualification in six.
1950 was a vacation year for Moore, by his standards. He only had two fights, winning both, including a 10 round decision in a rematch with Lydell.
In 1951, Moore boxed 18 times, and he won 16, lost 1 and drew one of those bouts. He went on an Argentinian tour, fighting seven times there, winning six and drawing one. In between those seven fights, he also had a trip to Montevideo, Uruguay, where he defeated Vicente Quiroz by a knockout in six. He knocked out Bivins in nine, and split two decisions with Johnson.
1952 was one of the most important years in Moore's life. After beating Johnson, Jimmy Slade and Clinton Bacon, knocked out in four in a rematch, the seemingly inevitable happened, as Moore was given an opportunity for the world title by world Light Heavyweight champion Joey Maxim, who had just defeated Sugar Ray Robinson by a knockout in 14. Moore became world champion by beating Maxim by a decision in fifteen rounds, finally reaching his dream of becoming a world boxing champion, at the age of 39 and 16 years after beginning his professional boxing career.
He won all nine of his bouts in 1953, including a 10 round non title win against fringe contender Nino Valdes of Cuba, and a 15 round decision over Maxim in a rematch to retain the belt. He made two more bouts in Argentina before the end of the year.
In 1954, he made four more fights, retaining the title in a third fight with Maxim; who once again went the 15 round distance, and versus Johnson, knocked out in 14. He also beat Bob Baker that year. In 1955, he beat Valdes again, and Carl Bobo Olson by a knockout in three, to retain the title. Olson was the world's Middleweight champion, and he had gone up in weight to challenge Moore. Next, it was Moore's turn to go up in weight and challenge the bigger champion, when he stepped into the ring with Rocky Marciano, world Heavyweight champion. Moore was within seconds of becoming world Heavyweight champion by dropping Marciano in round two, but Marciano recovered and knocked Moore out in the ninth to retain the belt.
In 1956, he went back to the Light Heavyweight division, and won 13 fights in a row, including a 15 round decision to retain the world's crown against Yolande Pompey in London, before going up in weight once again, and challenging for the world Heavyweight crown. This time, it was for the title left vacant by Marciano, and Moore lost to Floyd Patterson by a knockout in five. Patterson made history that night, becoming, at the age of 20, the youngest world Heavyweight champion in history, record which he would hold until 1986.
Moore went down to the Light Heavyweights once again, and won all six of his bouts during 1957. He retained the title against Tony Anthony by a knockout in seven, and had two fights in Germany and one in Canada.
In 1958, Moore had 10 fights, going 9-0-1 during that span. His fight with Yvon Durelle in particular, was of note. Defending his world Light Heavyweight title in Montreal, he was dropped twice in round one, and once in round five, but dropped Durelle in round 10 and won by a knockout in the 11th. That fight has come out among the greatest fights of all time on many books, and it has become a regular fight on ESPN Classic's boxing shows.
In 1959, he only had two bouts, beating Sterling Davis by a knockout in three, and then beating Durelle, also by a knockout in three, in a rematch, to once again retain his world Light Heavyweight title.
During 1960, he was stripped of his world Light Heavyweight title by the National Boxing Association (NBA), but he won three of his four bouts that year, his lone loss coming versus Giulio Rinaldi by a decision in 10 at Rome.
The NBA promptly re-instated him as world Light Heavyweight champion in 1961, and he won two fights before defending his crown for what would turn out to be his last time: He beat Rinaldi by a 15 round decision to retain the belt. In his last fight that year, he once again ventured into the Heavyweights, and met Pete Rademacher, a man who had made history earlier in his career by becoming the first man ever to challenge for a world title in his first professional bout (when he lost to Patterson by a knockout in six). Moore beat Rademacher by a knockout in nine.
In 1962, he was stripped again of his world Light Heavyweight title, this time for good. He decided to campaign exclusively as a Heavyweight from there on, and beat Alejandro Lavorante by a knockout in 10 and Howard King by a knockout in one at Tijuana. Then, he drew with former world Light Heavyweight champion Willie Pastrano in 10, and, in his last fight of note, he faced Cassius Clay, then a young Heavyweight out of Louisville. He was beaten by a knockout in four rounds in that fight.
Despite retiring, he couldn't escape the limelight, being the recipient of numerous awards and dedications afterwards. In 1965, he received the key to the city of San Diego. In 1970, he was chosen as the Man of The Year by Listen Magazine, and he received the key to the city of Sandpoint, Ohio.
He was elected in 1985 to the St. Louis city boxing hall of fame, and he received the Rocky Marciano memorial award in the city of New York in 1988. In 1990, he became a member of the International Boxing Hall Of Fame in Canastota, being one of the original members of that institution. He was the oldest boxer to win the world's Light Heavyweight crown, and is believed to be the only boxer to have boxed professionally in the eras of Joe Louis, Marciano and Clay/Muhammad Ali. He was one of a handful of boxers whose careers spanned four decades, and he had a final record of 181 wins, 24 losses, 9 draws and 1 no contest, with 145 official knockout wins.