George Brett was the second youngest child of a sports-minded family which included his older brother Ken, a major-league pitcher. His family moved to the midwest and later to Southern California when he was a boy, and Brett grew up hoping to follow in his brother's footsteps as a big-league baseball player. He was drafted by the fledgling Kansas City Royals in the second round of the 1971 baseball draft.

Brett began his professional career as a shortstop, but had trouble going to his right defensively and was soon shifted to third base. As a third baseman, his powerful arm remained an asset, and he remained at that spot for 15 years. The Royals promoted him to the major leagues on August 2, 1973.

He won the starting third-base job a year later, but struggled with the bat until he asked for help from Charlie Lau, the Royals' hitting instructor. Spending the 1974 All-Star break working together, Lau taught Brett how to protect the entire plate and cover up some holes in his swing that experienced big-league pitchers were taking advantage of. Armed with this knowledge, Brett developed rapidly as a hitter.

He topped the .300 mark for the first time in 1975 with a .308 mark, then won his first batting title in 1976 with a .333 average. The four candidates for the batting title that year were Brett and Royals teammate Hal McRae, and Minnesota Twins teammates Rod Carew and Lyman Bostock. In dramatic fashion, Brett went 2 for 4 in the final game of the season against the Twins, beating out his three rivals, all playing in the same game. His lead over second-place McRae was less than .001.

A year later, Brett emerged as a power hitter with 22 home runs helping the Royals to another American League Championship Series, 1977, and proceeded to have an incredible 1979 season in which he was an MVP candidate. He became the first player in league history to have at least 20 doubles, triples and homers all in one season (42-20-23) and led the league in hits, doubles and triples while batting .329.

All these impressive statistics were just a prelude to 1980, when Brett nearly matched Ted Williams' feat of batting .400. He was at or above .400 as late in the season as September 19 before settling at .390, the modern record for the highest average ever by a third baseman. This time, there was no doubt Brett was the league MVP.

In the 1980 postseason, Brett led the Royals to their first pennant, sweeping the playoffs in three games from the rival New York Yankees who had beaten K.C. in the 1976, 1977 and 1978 playoffs. In Game 3, Brett hit a ball into the third deck of Yankee Stadium off superstar closer Goose Gossage, a longtime rival. Long-time announcer Howard Cosell commented on the broadcast "...it looked like Gossage let up on that pitch that Brett hit out, and Brett made him pay for it." A few seconds later the ABC radar gun showed the pitch's speed at 98 mph, Gossage's fastest pitch of the game by 2 mph. Brett then hit .375 in the 1980 World Series, but the Royals lost in six games to the Philadelphia Phillies. During the 1980 World Series, Brett made headlines for reasons other than his play on the field. After Game 2, Brett had to have surgery to remove hemorrhoids. In Game 3, a fully recovered Brett hit a home run as his Royals wound up winning in 10 innings by the score of 4-3.

In 1985, Brett had another brilliant season in which he helped to propel the Royals to their second pennant. He batted .335 with 30 home runs and 112 RBI, finishing in the top 10 of the league in 10 different offensive categories. In the final week of the regular season, he went 9-for-20 at the plate with 7 runs, 5 homers, and 9 RBI in six crucial games, five of them victories. He was MVP of the 1985 playoffs against the Toronto Blue Jays, leading K.C. back from a 3-1 deficit in games, and then batted .370 in the World Series against the St. Louis Cardinals, as the Royals again rallied from a 3-1 deficit to become world champions.

In 1988, Brett moved across the diamond to first base in an effort to reduce his chances of injury and had another MVP-calibre season with a .306 average, 24 homers and 103 RBI. But after batting just .290 with 16 homers the next year, it looked like his career might be slowing down. He got off to a terrible start in 1990 and at one point even considered retirement. But his manager, former teammate John Wathan, encouraged him to stick it out. Finally, in July, the slump ended and Brett batted .386 for the rest of the season. In September, he caught Rickey Henderson for the league lead, and in a battle down to the last day of the season, captured his third batting title with a .329 mark. This made him the first, and only to this date, player in history to win batting titles in three decades.

Brett played three more seasons for the Royals, mostly as their designated hitter, but occasionally filling in for injured teammates at first base. He passed the 3,000-hit mark in 1992 and retired after the 1993 season. In his final at-bat, he hit a double up the middle against Rangers closer Tom Henke and scored on a home run by teammate Gary Gaetti.

The Kansas City Royals have retired Brett's number 5.

His 3,154 career hits are the most by any third baseman in major league history, and 15th all-time. Baseball historian Bill James regards him as the second-best third baseman of all time, trailing only his contemporary, Mike Schmidt. Brett was elected to the Hall of Fame in 1999, with the fourth-highest voting percentage in baseball history, receiving a higher percentage of the vote than Babe Ruth, Hank Aaron, Willie Mays, Stan Musial, Ted Williams, and Joe DiMaggio. That same year, he ranked Number 55 on The Sporting News' list of the 100 Greatest Baseball Players, and was nominated as a finalist for the Major League Baseball All-Century Team.

Following the end of his baseball career, Brett became a vice president of the Royals and has worked as a part-time coach, as a special instructor in spring training, filling in as the batting coach, and as a minor league instructor dispatched to help prospects develop. In 1998, an investor group headed by Brett and his older brother, Bobby, made an unsuccessful bid to purchase the Kansas City Royals.