College soccer and move to Europe Onyewu grew up in the
Washington, D.C. suburbs of
Silver Spring and
Olney, Maryland, where he attended St. Andrew Apostle School and
Sherwood High School. Onyewu enrolled in the
U.S. residency program in
Bradenton, Florida, before returning to Sherwood to graduate. He then played two years of
college soccer at
Clemson University in South Carolina. He moved to Europe in 2002, signing with
Metz of
Ligue 2 in France. In 2003, he was loaned out to
La Louvière in Belgium.
Standard Liège and Newcastle Onyewu was loaned to
Standard Liège in 2004. The move to Liège was made permanent for the
2004–05 season. After the season, he was named to the Belgian league's Best XI as well as Foreign Player of the Year for 2005. Having been the subject of many transfer rumors regarding clubs throughout Europe, Onyewu finally completed a loan deal with
Newcastle United in January 2007, covering the remainder of the
2006–07 season. He made his debut for Newcastle against
Fulham on February 3, and his home debut a week later, alongside
Titus Bramble, in a 2–1 victory over
Liverpool. The two formed an ill-fated partnership, making a number of costly mistakes which was ultimately to cost Onyewu his place. Following the arrival of new manager
Sam Allardyce, Onyewu fell out of favor, and Newcastle decided not to make the loan deal permanent. Onyewu returned to Standard, and his play continued to improve. He made his 100th
Belgian First Division appearance for
Standard Liège on March 14, 2008, against
Germinal Beerschot, and was an integral part of the club as they went on a 29-match unbeaten streak to win the
2007–08 Belgian First Division. After the season, he was named to the Belgian league Best XI for the second time. His strong form continued during the
2008–09 season. He led the Standard defense to a second consecutive Belgian league title. Standard was drawn with
Anderlecht at season's end, and Standard won a
two-legged playoff for the championship. Onyewu dealt with racism during his time in Belgium, even having been punched and shouted at by racist fans while playing for Standard Liège. The most well-publicized incident occurred in the
2008–09 Championship playoff when
Anderlecht defender
Jelle Van Damme, according to Onyewu, allegedly repeatedly called him a "dirty ape," Van Damme denied the accusations following the match and in return said that Onyewu himself taunted him in a racist way by calling him "dirty Flemish." Approximately two weeks later, Onyewu's lawyer announced that he was suing Van Damme in an effort to end on-field racism in European soccer. The case was withdrawn in February 2011 after a meeting between the two players when Van Damme apologized for any offense he may have given.
Milan and loan spell with Twente Onyewu signed a three-year contract with
A.C. Milan in July 2009, but never played a league game in his eighteen-month spell at the club. He made his debut on September 30 as a substitute in a
Champions League loss to
Zürich at
San Siro. Onyewu missed all the
2009–10 season—appearing in only one Champions League match—due to a knee injury suffered while on national team duty. At the end of the season, it was announced that Onyewu's contract with Milan was extended by one season, keeping him under contract with the club until the end of the 2012–13 season. Upon Onyewu's request, the one-year extension included no salary. On November 5, 2010, Onyewu made international headlines when he and teammate
Zlatan Ibrahimović engaged in a fight during training, before a league match against
Bari. It was reported that Onyewu suffered a reckless tackle from Ibrahimović, causing Onyewu to confront him. The two were then separated by teammates, though the club reported he and Ibrahimović have made up for their fight. In January 2011, Onyewu joined Dutch side
Twente on loan until the end of the season. Onyewu made his debut for the
Tukkers on the January 19 against
Heracles Almelo in an
Eredivisie fixture where he would play the full 90 minutes. Despite his stay being short lived at the Dutch side, Onyewu would feature predominantly in both domestic competitions and European competitions where his side reached the quarter finals. His stint with Twente saw him accumulate 14 appearances, as well as pick up a cup winners medal after Twente defeated
Ajax 3–2 in the
KNVB Cup final.
Spells in Portugal and Spain In June 2011, Onyewu joined Portuguese side
Sporting CP on a free transfer where he signed a three-year deal from
A.C. Milan. In Sporting CP's first five competitive games of the season, three Primeira Liga and two European qualifying matches, Sporting manager
Domingos Paciência opted to start central defenders
Daniel Carriço and
Alberto Rodríguez alongside
Ânderson Polga, which left Onyewu on the bench. Injuries during the start of the season to Carriço and Polga led to manager Domingos Paciência starting Onyewu in Sporting's line-up. Onyewu made his team debut on the September 10 in a 3–2 away victory over
Paços de Ferreira where he would play the full 90 minutes. He scored his first goal for Sporting CP against
Rio Ave at the
Estádio dos Arcos on September 19, a week after making his Sporting CP debut, in a 3–2 win in which Onyewu scored the winning goal from a header after a
Diego Capel corner kick found him unmarked in the penalty area. Unlike his time with A.C. Milan, Onyewu's playing time increased during the 2011–12 season. During the season, he gradually established himself as the first team regular starter, playing as a center-back alongside
Ânderson Polga. Despite the sacking of Domingos Paciência and the introduction of
Ricardo Sá Pinto as Sporting manager in early 2012, Onyewu remained a first team regular until mid February where he sustained an injury in a league match against
Paços de Ferreira. Onyewu's injury, which turned out to be an internal lateral ligament and an external meniscus fracture to his right knee, kept the American out of action for two months. Onyewu's recovery saw him back in late April where he played his first match in two months against
Nacional. Onyewu's recovery meant he would be available to compete in the
2012 Taça de Portugal Final where his side would come up on the losing end against
Académica de Coimbra. Onyewu finished his first season with the
Leões with 31 appearances to his name, and scoring five goals. The appointment of
Ricardo Sá Pinto as Sporting manager led to the arrival of
Khalid Boulahrouz and
Marcos Rojo, which saw Onyewu loaned out to Spanish
La Liga outfit
Málaga in August 2012. Onyewu made his team debut on October 24 in a
UEFA Champions League match as a substitute in a 1–0 victory over his former side
A.C. Milan. A week later, he started and scored his first Málaga goal against
CP Cacereño on October 31 in a fourth-round
Copa del Rey tie. Onyewu's goal-scoring form continued in the same competition against
SD Eibar on December 18, where his stoppage time goal earned his side a draw. However, Onyewu's stay with
Málaga proved to be unsuccessful as he struggled to establish himself as a first-team regular and only managed to play nine matches all season, contributing two goals. Onyewu returned to Sporting in the summer of 2013 but agreed to a contract termination by mutual consent.
Return to England and beyond In October 2013, Onyewu signed with
Queens Park Rangers on a free transfer, but he failed to make any appearances and was an unused substitute on six occasions. In January 2014, Onyewu joined
Sheffield Wednesday until the end of the season. In October 2014, Onyewu signed for
Charlton Athletic on a short-term contract, making his debut as a substitute on December 26. The club extended his contract through the end of the season, but he was released following the conclusion of the season. Onyewu was released at the end of his contract in May 2015. Onyewu trialed with
Major League Soccer's
New York City FC in May 2015 but was not signed. He later spent a preseason tour with
Rangers of the
Scottish Premiership in June 2016 but was not offered a contract.
Return to America Onyewu signed with the
Philadelphia Union during the 2017 MLS preseason. Originally brought in to be a veteran presence for a young backline Philadelphia, Onyewu became a regular starter for the Union earning 22 appearances and scoring once. Onyewu was released by the Union at the conclusion of the
2017 season.
Retirement In September 2018, Onyewu announced his retirement from professional soccer via
Instagram concluding a 15-year career. ==International career==