Mohamed Kallon attended primary school in Kenema and completed his secondary education at St. Edwards Secondary School in Freetown.

During his early international career for Sierra Leone, Kallon was given the nickname Small Kallon by Sierra Leonean football fans because he was the youngest of the three Kallon brothers in the Sierra Leone national

After he completed his form three levels of education (grade 9 in the U.S.) from St. Edwards Secondary School in Freetown in 1994, Kallon signed with the local club, Old Edwardians of the Sierra Leone National Premier League at the age of 15. During the 1994–95 season, he struck fifteen goals in 24 league games for Old Edwardians and became the youngest player to ever play and score in Sierra Leone National Premier League.

After the 1994–95 season, Kallon left Old Edwardians and signed for Lebanese club Tadamon Sour. Mohamed Kallon is indeed spotted by Ali Abdullah, while playing a game with friends, on a beach in Freetown. Son of a Lebanese diplomat living in Sierra Leone – Lebanon then already had many businessmen in West Africa – Abdullah praised Kallon’s qualities to several relatives, and managed to obtain several trials for him in Lebanon.

Eager to discover foreign countries, and pushed by his father, Mohamed Kallon accepts the offer and travels with Ali Abdullah, only 15 years old. First on the side of Ajman, where the test turns out to be inconclusive, before finally catching the eye of the staff of Tadamon Sour, the club from the city of Tire. Kallon will thus spend the 1994-1995 season there, scoring 15 goals in 24 games, despite six difficult first months, due in particular to the cold Lebanese winter.

He spent one season with Spånga IS in Stockholm, Sweden. He was then signed by Inter Milan. He was then loaned to Swiss Super League club AC Lugano, Serie A club Bologna F.C. 1909 and Cagliari, and Serie B clubs Genoa He also farmed to Reggina and Vicenza in a co-ownership deal for an undisclosed fee and 9,000 billion lire respectively (€4,648,112). He played with Cristiano Zanetti at Cagliari, whom he later worked with again at Inter Milan.

Inter Milan

2001–02

After the abolition of the non-EU quota for each team halfway through the 2000–01 season,Kallon returned to Italian club Inter Milan before the start of the 2001–02 season, for a reported 8,500 billion lire transfer fee (€4,389,884).[9] With Christian Vieri, Ronaldo, Álvaro Recoba, Adriano, Hakan Şükür and Nicola Ventola also in the side, Kallon was originally a third or fourth choice striker. But injuries to Ronaldo and Recoba meant that Kallon played 29 Serie A matches, scoring 9 goals and becoming the team’s second highest scorer of the 2001–02 Serie A season, behind Vieri, as the club narrowly missed out on the league title, finishing in third place, also reaching the semi-finals of the UEFA Cup.

2002–03

He played nine times scoring five goals in Serie A in 2002–03 season due to injuries in August[10] and February, as the team managed a second-place finish in the league. Kallon returned to the side in May after Gabriel Batistuta was injured in April. He also played both legs of the 2002–03 UEFA Champions League semi-final against A.C. Milan as Batistuta was unable to register. He played in both games as a second-half substitute, for Álvaro Recoba and Hernán Crespo respectively.

2003–04

Kallon tested positive for the banned substance nandrolone after the Serie A match against Udinese Calcio on 27 September 2003[12] and was banned from football for eight months. Kallon then struggled to get into the starting eleven during the 2003–04 season, primarily due to the rise of young Nigerian striker Obafemi Martins and the return of Brazilian ace Adriano.

Monaco

Kallon signed a four-year contract with Monégasque club AS Monaco before the start of the 2004–05 season, as the UEFA Champions League runners-up had lost Dado Pršo and Fernando Morientes.He was impressive during his first season at Monaco, but quickly fell out with French manager Didier Deschamps, and was relegated to the bench in March 2005.

He moved on loan to Saudi club Al-Ittihad on 29 July 2005.He helped the team win the 2005 AFC Champions League, leading the competition with six goals scored, including goals in each legs of the semi-final and final respectively. He also played at the 2005 FIFA Club World Championship with Al-Ittihad before returning to Monaco in 2006.

He played 12 Ligue 1 matches in his last full season with Monaco during the 2006–07 campaign. He played his last match in league play on 11 August 2007 against FC Lorient, the second match of the season, before he was released by Monaco. He underwent a trial with Birmingham in September 2007,after previously being linked with Derby County in July.However, Kallon failed to qualify for a work permit in England, as Sierra Leone ranked 79th in the FIFA World Rankings in September 1997, but the requirement was above 70th for non-EU internationals. In November 2007, he signed a pre-contract with Al Hilal,but this later collapsed.

AEK Athens

Kallon signed a six-month contract with Greek club AEK Athens on 29 January 2008.[20] He played for the capital club in the UEFA Cup 2007–08 round of 32 against Getafe, but AEK lost 4–1 on aggregate, with no goals from Kallon. He also played in the Super League Greece playoffs to determine qualification to European competition. He scored once in his three appearances, and AEK finished second to qualify for the following year’s UEFA Cup.

Greek fans remember him especially for an excellent goal against PAOK in a 4–0 win, when he scored with a chip shot outside the box.

Al-Shabab

He moved to Al-Shabab of the United Arab Emirates in 2008. He was released after picking up a serious injury in an international match.

Kallon FC

In October 2009, he signed for his own club Kallon FC.

Later career

On 1 March 2010, he joined the Chinese championship, signing a one-year deal with Shaanxi Baorong Chanba.Kallon made his CSL debut against Dalian Shide on 28 March and scored a penalty kick in 50th minute.He decided to leave after his contract was finished in December to be closer to his family.In 2011, he moved to India and signed with I-League club Chirag United Kerala.

He returned to Kallon F.C. ahead of the 2012 CAF Confederation Cup,and scored the winning goal that got them to the second round.

On 26 June 2014, was named the head coach of Sierra Leone u-17 side.

On 22 March 2016, he announced his retirement as a player, having last played in 2014.

International career

Kallon became the youngest player to ever play for the Leone Stars when he made his senior international debut for Sierra Leone at the age of fifteen in April 1995 against Congo in the 1996 African Cup of Nations qualifier in Freetown, in which he scored the winner. At the age of 16, Kallon was the youngest player at the 1996 African Nations cup in South Africa. He scored one of his country’s two goals as Sierra Leone defeated Burkina Faso 2–1 in their opening group match at the 1996 African Nations Cup, played at the Free State Stadium in Bloemfontein, South Africa.

Since then, he is the key member of Leone Stars and active at 1998, 2002, 2006 and 2010 World Cup qualification. His most recent cap is on 9 February 2011 against Nigeria in a friendly. Kallon was the captain of the Sierra Leone national team but quit his captaincy after the team failed to qualify for the 2010 FIFA World Cup and the 2010 African Cup of Nations.