Chepkok wuxuu ku dhashay Kapkitony oo ku taal Degmada Keiyo ee Gobolka Rift Valley ee Kenya. Wuxuu ku guuleystay billaddii lacagta ahayd ee tartankii da'yarta ee 2007 World Cross Country Championships
, ayaa kaalinta sagaalaad ka galay tartankii Adduunka ee 2009 iyo kaalinta toddobaad ee Finalkii Adduunka ee 2009. Wuxuu ku guuleystey guul weyn oo 5000 m ah oo ka soo baxday IAAF Diamond League circuit 2010, isagoo ku guuleystey British Grand Prix.