In 1926, Louis' family joined the African-American migration from the rural South to the urban North. They settled in Detroit and that was where he grew up. As a teenager he worked odd jobs and began boxing with neighborhood kids. Louis used the 50 cents a week his mother gave him for violin lessons to rent a locker at the Brewster Recreation Center, where he began a successful amateur boxing career.

John Roxborough, the illegal numbers betting king in Detroit's black ghetto, decided to sponsor Louis's professional career. He enlisted the help of Julian Black, a Chicago speakeasy owner and numbers operator, and they moved Louis to Chicago to train with Jack Blackburn, a former lightweight boxer and skilled trainer who had already taken two white fighters to world championships in lower weight divisions. Blackburn patiently taught Louis a fundamental style of boxing that emphasized balanced but unspectacular footwork, a strong left jab, counterpunching, and throwing combination punches in rapid sequence. Until his death in 1942, Blackburn ensured that Louis ran six miles a day, sparred with discipline, and maintained his physical superiority and confidence against all challengers.

By March 1935, Louis had won 18 professional fights and was bumping up against the barrier of segregation. Denied economic opportunity and political power, African Americans were invisible in America's emerging media age. With the exception of occasional tokens in track and field and college football, blacks had no opportunities to participate in major sports. In boxing, Louis had to live down the legacy of Jack Johnson, the first black heavyweight champion, who had caused race riots by humiliating former champion Jim Jeffries and national outrage by marrying white women. After Johnson lost his title in 1915, white promoters and fighters denied black contenders the opportunity to fight for the heavyweight title.

Mike Jacobs, a Jewish immigrant, helped Louis permanently trample the color line. Jacobs needed a heavyweight contender to break the Madison Square Garden Corporation's monopoly on big-time boxing and promised Louis that he would not have to throw fights to white opponents and would eventually get a chance at the title. Jacobs promoted five Louis tune-up fights then brought Louis to New York City for a fight against former heavyweight champ Primo Carnera in June 1935. Jacobs skillfully played on Louis' role as an ambassador for his race in the buildup to the Carnera fight, and when Louis destroyed his opponent in six rounds, he became a media sensation.

On September 24, 1935, Louis married Marva Trotter in a brief private ceremony at a Harlem apartment and then drove to Yankee Stadium to fight Max Baer before a crowd of 80,000 people. Although Baer was regarded as the best white fighter in the world, Louis knocked him out in the fourth round. Louis suddenly was one of the most famous men in the world. The way white sportswriters wrote about Louis reveals how novel it was for a black to reach a position of prominence. Most journalists of the day constantly mentioned Louis's race and gave him nicknames, such as the Brown Bomber, the Dark Destroyer, and the Tan Tornado.

Due to the fact that Louis was the only black in the white world of fame and fortune, he became the symbol of his race to blacks and whites alike. For African Americans, Louis was the greatest of their heroes. Every time he stepped into the ring against a white opponent, Louis refuted theories of white superiority. After every Louis victory, blacks in urban ghettos across the United States filled the streets to cheer their hero. Louis lost his reputation for invincibility on June 11, 1936, when he suffered his first professional loss to Max Schmeling of Germany. Mike Jacobs outmaneuvered Schmeling and the Madison Square Garden Corporation by offering the heavyweight champion, James J. Braddock, a share of future promotional income from Louis' fights. Braddock agreed to defend his title against Louis instead of Schmeling. On June 22, 1937, in Chicago's Comiskey Park, Louis knocked out the courageous but overmatched Braddock in eight rounds. Despite this victory, sports fans would have doubts about Louis's abilities until his rematch with Schmeling, the only man who had beaten him. Jacobs scheduled their rematch for June 22, 1938 in Yankee Stadium. The fight that would define Louis' career was also one of the most symbolic sporting events in history.

Whites accepted Joe Louis as the representative of American values fighting against a symbol of Nazi racism. Upset with himself for losing to Schmeling in their first fight, angry that many people still believed that Schmeling was his boxing equal, determined to win a symbolic victory and personal vindication, Louis decided on a strategy that fit his mood. He planned to attack without letup, not allowing Schmeling to set himself long enough to counterpunch with a right over Louis' jab, as Schmeling had done so successfully in their first fight. In the first round, Louis immediately drove Schmeling against the ropes with a sequence of combination punches and then landed an overhand right that had Schmeling out on his feet. Schmeling instinctively turned to avoid Louis, and as he turned Louis broke two of Schmeling's vertebrae with a roundhouse right to Schmeling's side. Louis knocked Schmeling down three times in rapid succession, and Schmeling's trainer, Max Machon, threw in the towel and rushed into the ring to protect his fighter. Referee Arthur Donovan called the fight at two minutes and four seconds into the first round, with Schmeling on his knees. More than 70,000 fans at Yankee Stadium and a huge international press contingent had witnessed a dominating athletic performance from a once-in-a-generation talent.

From January 1939 until the United States entered World War II, Louis defended his title 15 times, fighting so often and so well that his overmatched opponents in early 1941 were called the "Bums of the Month." The only significant risk to Louis' title came on June 18, 1941, against light-heavyweight champion Billy Conn. Weighing 170 pounds to Louis' 200, Conn used his lightning-quick hands to build a solid lead on points against Louis going into the 13th round. But Conn went for a knockout, continuing to trade punches until Louis interrupted a Conn combination with an overhand right that was solid enough to slow Conn. A two-minute volley of punches finished Conn with two seconds left in the round.

In early 1942, just after the United States entered World War II, Joe Louis enlisted in the U.S. Army. He went on morale-boosting tours for the army throughout the war, fighting exhibitions in the United States, Alaska, and Europe, and quietly broke racial barriers in the segregated armed services wherever he went. After the war, the treatment of Louis by the white press changed. The alliterative nicknames disappeared, save the standard Brown Bomber and Dark Destroyer. White journalists now rarely identified him as a Negro and stereotyped references declined. Important newspapers praised Louis in editorials, and the praise had a more sincere and less condescending ring. Louis left the army in 1945 as a beloved patriot but a bankrupt one. He had always been generous and free spending to a fault. During the war he borrowed heavily from Mike Jacobs and John Roxborough, and he had a large deferred tax bill. After the war, income tax rates on the top brackets rose as high as 90 percent as the U.S. government tried to pay off the huge debt accumulated during the war.

On June 19, 1946, Louis knocked out Billy Conn in eight rounds in a much-anticipated rematch between two over-the-hill fighters. Louis' purse of $600,000 from the Conn rematch was a fantastic sum for those days but it was an illusion. Mike Jacobs arranged to have Louis first pay off his personal debts, leaving Louis with an even larger unpaid tax liability. With upper tax brackets so high, Louis was running in quicksand, sinking under a tax bill that was above $1 million by the mid-1950s (it was never repaid).

Louis defended his title twice against Jersey Joe Walcott before retiring for the first time in 1949. Financial problems forced him back into the ring against new champion Ezzard Charles on September 27, 1950; Charles won a 15-round decision. After a series of wins over lesser lights, Louis fought for the last time against future champion Rocky Marciano on October 26, 1951. Louis outpointed Marciano until the eighth round, when he ran out of gas and was knocked out.

Louis finished his career with 68 wins, 54 by knockout, and three losses.
Of the 43 men Louis fought before World War II, only one was black. The two heavyweight champions who followed him, Walcott and Charles, were black and were readily accepted by Americans as a result of Louis' well-crafted public image. Black athletes following his example had integrated the National Football League in 1945, Major League Baseball in 1947, and the National Basketball Association in 1949. Louis opened sports to blacks and helped to make athletics a cutting edge of the civil rights movement.

Louis's first wife, Marva, with whom he had two children, divorced him in 1945, remarried him in 1946, and divorced him again in 1949. During the 1950s Louis lived a nomadic existence, making money from personal appearances and a brief stint as a professional wrestler. He was married to Rose Morgan, a successful beauty shop operator, from 1955 to 1958. In 1959, he married Martha Malone Jefferson, a successful black attorney, and moved into her home in Los Angeles. Martha cared for him through bouts of paranoia and drug abuse. After an involuntary commitment in a Colorado mental hospital in 1970, Caesars Palace in Las Vegas offered Louis a house and employment as a greeter in its casino. Louis lived there until his death from a massive heart attack on April 12, 1981. Jesse Jackson, who would later be the first African American to run for the presidency of the United States, told 3,000 assembled mourners that with "fist and character," Louis had "snatched down the cotton curtain."

Louis had followed a strategy of not speaking out against America's unrelenting racism in the 1930s in order to win white acceptance. In part because of the success of that strategy, white America became more aware of its own racism. In time, many African Americans became famous in sports, politics, and the arts, and the white media slowly came to accept black celebrities who spoke out against racism and refused to conform to stereotypes. A growing black militancy and rising white consciousness fed each other. In such a context, Joe Louis's image as inoffensive and popular with whites seemed dated and less worthy of respect.

Louis not only had to establish himself as a dominant athlete, but he also had to prove that blacks could compete on equal terms with dignity and without exacerbating racial tensions. Louis accepted that responsibility and performed so well that he became a challenge to segregation.