Martin was born in Saginaw, Michigan on December 30, 1977 to Lydia Moore, a single mother of two. He has a sister, Tamara, who is 3 1/2 years older. Shortly after, the family moved south to the Oak Cliff neighborhood of Dallas, where she worked two jobs. Later, Kenyon was often watched by his sister while their mother worked.
He stuttered as a child, and attended three high schools in four years, but he sought refuge in sports, playing basketball, baseball, and football. In high school, many major universities showed interest in his basketball prowess, but the University of Cincinnati and assistant coach John Loyer recruited him hardest after seeing him play AAU ball after his junior year. He graduated from Bryan Adams High School in Dallas in 1996 (he was named to the school's hall of fame in 2009).
He went to the University of Cincinnati and played for the Cincinnati Bearcats under the direction of head coach Bob Huggins. He was homesick early in his freshman year and actually took a bus back to Dallas. But his mother as well as his older sister, who by then was working two jobs and attending college, steered him to return to school.
By the time he was a junior, he led Cincinnati to a 27-6 record and was named second-team All-Conference USA and, in the summer following, he led the U.S. team to the gold medal in the World University Games, leading the team in scoring and rebounding.
As a senior in 1999–2000, he averaged 18.9 points, 9.7 rebounds and 3.5 blocks per game during a season in which the Bearcats were ranked #1 for 12 weeks. That season, he recorded his second triple double with 28 points, 13 rebounds, and 10 blocks vs. Memphis (in 1997, he recorded 24/23/10 vs. DePaul). Martin was the consensus National Player of the Year, earning numerous awards from various organizations, and the team was ranked #1 in the nation at the conclusion of the regular season. However, Martin suffered a broken leg three minutes into the Bearcats' first game of the Conference USA Tournament, keeping him out of the NCAA Tournament that year. The team finished with a record of 29-4.
He remains the Bearcats' all-time leader in career blocked shots (292) and field goal percentage (.586). Cincinnati retired his #4 jersey on April 25, 2000. Later that year, Martin was selected first overall in the 2000 NBA draft by the New Jersey Nets. Martin is currently the last American-born college senior to have been the top overall pick.
Martin graduated with a Bachelor's Degree in Criminal Justice.
As a rookie for the New Jersey Nets, Martin averaged 12 points, 7.4 rebounds and 1.7 blocks per game. He was named to the NBA All-Rookie First Team and finished second in voting for NBA Rookie of the Year. In his second season, Martin averaged 14.9 points, 5.3 rebounds, 1.3 steals and 1.7 blocks per game in helping the Nets rise from last place in the Atlantic Division to an Eastern Conference title and the best season to date in the Nets' NBA history. Along with Jason Kidd, Kerry Kittles, Keith Van Horn and Richard Jefferson, Martin led the Nets to the 2002 NBA Finals, where they were swept by the Los Angeles Lakers. In his third season Martin again helped his team into the NBA finals, where the Nets lost in six games to the San Antonio Spurs. The next year, Martin averaged 16.7 points, 9.5 rebounds and 1.3 blocks en route to his first NBA All-Star selection, as a backup forward for the Eastern Conference All-Stars. In the 2004 NBA All-Star Game, Martin scored 17 points, grabbed 7 rebounds and had 3 assists.
Martin and teammate Alonzo Mourning almost fought when Martin mocked Mourning's life-threatening kidney disease. Martin later admitted that he had made a mistake and apologized to Mourning, and Martin now participates in Mourning's annual charity basketball game (see below "Off the court").
At the end of the 2003–04 season, Martin was traded to the Denver Nuggets for three future first-round draft picks in a sign-and-trade deal.
Martin played in 70 games during the 2004–05 season, averaging 15.5 points and 7.3 rebounds; however, a problem with his knee was detected shortly into the off-season, and on May 16, 2005, Kenyon underwent microfracture surgery on his left knee.
During the 2005–06 season, Martin missed 26 games due to knee tendinitis, but was able to return in time for the playoffs. During that playoff series against the Los Angeles Clippers, Martin was suspended from the Denver Nuggets indefinitely for "conduct detrimental to the team." During halftime of game two of the first round series, Martin got into an argument with head coach George Karl over his playing time, and refused to play for the second half of the game. During the offseason, Karl and Martin apparently "patched things up."
Believing injuries were behind him, Martin learned the swelling now occurring in his right knee would require another microfracture procedure. On November 15, 2006, after playing two regular season games, Martin underwent his second knee operation in less than two years. Martin is believed to be the first NBA player to have, and to return from, microfracture surgery on both knees.
Martin was fined $15,000 by the NBA when, during the third quarter of a 2006 game against the Chicago Bulls, Martin as well as some of his friends got into a verbal altercation with some fans. He was also cautioned to no longer bring his entourage to games.
To symbolize a fresh start to his career, Kenyon changed his uniform number from 6 to the number 4, which he wore in college, for the 2007–08 season.
Martin became an unrestricted free agent in the summer of 2011; however, due to the 2011 NBA lockout, he opted to sign a one-year contract with the Xinjiang Flying Tigers of the Chinese Basketball Association. His contract reportedly would have made him the highest paid player in the Chinese league's history. On December 24, 2011, Martin was released from the club so that he could "take care of family affairs". Martin was initially not allowed to return to the NBA until the Flying Tigers' season ended on February 15, 2012, if not later due to the 2012 CBA Playoffs. However, the International Basketball Federation (FIBA) granted him an earlier release on February 2.
On February 3, 2012, Martin signed with the Los Angeles Clippers. In his first game with the Clippers, Martin scored 6 points and collected four rebounds in a loss to the Cleveland Cavaliers.
On February 21, 2013, Martin agreed to join the New York Knicks on a 10-day contract, which reunited him with Jason Kidd. He officially joined the team on February 23. He was signed to a second 10-day contract on March 5, and signed for the remainder of the season on March 15. Upon his signing, he provided a large amount of help to a Knicks team that was depleted in the frontcourt, replacing Tyson Chandler, who was out with a neck injury, in the Knicks' starting lineup. On July 25, 2013, Martin re-signed with the Knicks for the 2013–14 season.
On January 9, 2015, Martin signed a 10-day contract with the Milwaukee Bucks. He made his Bucks debut later that night, recording 6 points, 2 rebounds and 1 block in the 98-84 win over the Minnesota Timberwolves. He went on to sign a second 10-day contract with the Bucks on January 19, and for the rest of the 2014–15 season on January 29.
On February 19, 2015, Martin was waived by the Bucks.
On July 3, 2015, Martin announced his retirement from professional basketball.
Martin is the half-brother of former Colorado Buffaloes shooting guard Richard Roby. He is also the cousin of Robert "50" Martin of AND1 Mixtape Tour fame.
Martin has three children: two sons, Kenyon Jr. and Kamron; and one daughter, Cierra Reign.
Martin started The Kenyon Martin Foundation to provide for families in need, especially those without a father figure in their lives. According to the foundation's website, organizations receiving grants (many in the Denver and Dallas areas) include All for One and One for All, American Institute for Stuttering, Bryan Adams High School (his alma mater), Colorado HAWKS (Hard At Work Kids) to "create an opportunity and an alternative to gangs for at-risk, disadvantaged youth", The Children's Museum of Denver, Denver Rescue Mission, Ludacris Foundation Helping Youth Help Themselves initiative, SafeHaven of Tarrant County domestic violence shelter for women, The Salvation Army, The Bridge Project, Third Way Center "providing mental health treatment in a residential setting for troubled teens", and Warren Village that helps "low-income single-parent families achieve sustainable personal and economic self-sufficiency." The foundation also runs the Hoops for Kids Basketball camp.
He has been active in support of non-profit The Stuttering Foundation of America since 2005, and in 2008 he was a recipient of the Freeing Voices, Changing Lives Leadership Award from the American Institute for Stuttering, for which he serves on the board of directors. He has served as honorary Ambassador for the March of Dimes Colorado Chapter to raise awareness about premature birth. He plays in the annual The Summer Groove in Miami, a charity event benefitting Alonzo Mourning Charities and Dwyane Wade's World Foundation. He also supports Special Olympics.
Martin has also been involved in philanthropic activities including donating $1,000 for each point and blocked shot in two games for the Asian tsunami relief efforts, buying the occasional home game ticket for less financially fortunate fans, and participating in number of campaigns like "Eat Right" and "Art of Sport."