Williams was born in Detroit, Michigan to an American father and a Filipina mother. He attended Martin Luther King High School where he earned four varsity letters in basketball under head coach Benny White in the Detroit PSL basketball league. He was elected the team's co-captain in 2000, the same year that he led the Crusaders to the state semi-finals. Williams is a two-time all-league honoree. As a senior, Williams was named an all-district and all-state player as he averaged 35 points, 14 rebounds, four blocks, three steals, and two assists per contest. During that time, the Crusaders were ranked in the state as high as number one, and was only defeated in the semi-final round of the state championships. Williams completed high school in 2000. During his four years, Martin Luther King had a 68–16 win-loss record.
College career
Williams attended Oakland University for four years, with the highlight of his career coming in his freshman year when the Grizzlies upset the University of Michigan.
2000–2001: Williams scored 18 points in Oakland's upset of Michigan on November 17, 2000. As a rookie, he ranked among the team leaders in scoring, rebounding, assists and steals.
2001–2002: Williams played in every game for the Golden Grizzlies as a sophomore.
2002–2003: Williams played in every game for a third straight year for OU in 2002–2003, finishing third on the squad in rebounding.
2003–2004: Williams had a solid senior season, ranking among the team leaders in scoring, rebounding, assists and steals.
College statistics
Amateur career
In 2004, Williams was spotted by then Philippine National Team head coach Chot Reyes after the latter liked the former's work ethic and style of play. Reyes invited Williams to try out for the Philippine Team. Williams agreed to it, ensuing his arrival at the local basketball scene. After displaying skills in exhibition games with the Philippine Team, he caught the attention of Filipino basketball aficionados, awarding him the title as the next big thing in Philippine basketball. Hence, he did not disappoint as he averaged 17.1 points and 12.8 rebounds during his stint with the Philippine Basketball League's Magnolia.
Professional career
When the Realtors took the first overall draft right in 2006, they did not hesitate to pick Kelly Williams over two-time UAAP MVP Arwind Santos, who was later picked second overall by the Air21 Express. During his rookie season, he normed averages of 17.3 points and 9.6 rebounds earning him the Rookie of the Year award, making him the second Realtor to do so after Jun Limpot in 1993. In his sophomore year, he improved his game immensely, helping his team win their second championship overall and grabbing the league's Most Valuable Player award along the way. In 2008, he was again named into the RP Training Pool under Coach Yeng Guiao. He was also entitled the PBA Most Valuable Player the same year. In 2009, during the All-Star Week, Williams was diagnosed of thrombocytopenia and was out for the remaining games of the entire conference. With his absence, his team did not last long and was eliminated by the Burger King Whoopers. He was also cut from the training pool for the national team because of his illness. In the middle of 2010 PBA Fiesta Conference, Williams, along with teammates Ryan Reyes and Charles Walters, was traded to the Talk N Text Phone Pals for Ali Peek, Nic Belasco, Yousif Aljamal, and Ogie Menor. The deal was brought about by Sta. Lucia's financial problems. Since joining Tropang Texters, in 2010, he won five championships. In 2011, Williams suited up and was the starting power forward for the Smart Gilas national basketball team, the national team of the Philippines who finished 4th in the 2011 FIBA Asia Championship.
Personal life
Williams suffers from idiopathic thrombocytopenic purpura. He was first diagnosed with the recurring rare blood disorder in 2009. Since then, he has been taking regular medications.
