[3] John played college soccer at Saint Louis University, and in the USL Premier Development League for Kansas City Brass.

[4][5] John was drafted by the Chicago Fire in the second round of the 2005 MLS SuperDraft and Led the team in scoring in the Lamar Hunt US Open Cup.

[6][7] On 7 August 2008, Randers announced that William had agreed to personal terms and joined Serbian SuperLiga team Čukarički Stankom.

[10] William's consecutive goal scoring run was abruptly ended by a slight meniscus tear against Khazar Lankaran.

[11] However, in January 2015 William left MAS Fez citing unpaid wages,[12][13] with a proposed move to League of Ireland powerhouse Shamrock Rovers falling through in February 2015.

[15][16] On September 14, 2015, William's two goals in a win against KTP propelled RoPS to top of the table for the first time in over 25 years.

He made his league debut in a match against NK Sesvete on December 4, 2021, a game in which Jarun won 4–3.

As of June 2009 William is eligible for selection by both the Nigerian and US National teams due to the new FIFA Regulations.