Rubuta ci gaba don wannan sakin layi - Niyonkuru ya fara halartar gasar kasa da kasa a gasar tseren tseren tseren kasa ta duniya ta 2005. Ya fafata a tseren matasa maza kuma ya gama na 33 daga cikin 'yan wasa 133 a cikin lokaci na minti 25 da dakika 32. A gasar Jeux de la Francophonie ta 2005, Niyonkuru ya yi gasa a tseren mita 10,000. Niyonkuru ya gama na huɗu a cikin lokaci na minti 29 da dakika 18.08, sakan 0.03 ne kawai a bayan wanda ya lashe lambar azurfa, ɗan Maroko Abderrahim Goumri. Niyonkuru sannan ya yi gasa a Gasar Zakarun Duniya ta 2006. Ya gama na biyar a cikin mita 10,000 a cikin lokaci na minti 28 da dakika 59.92. Ya kasance 6.63 seconds a baya ga mai nasara, Ibrahim Jeilan na Habasha. A shekara ta 2007, Niyonkuru ya yi gasa a Gasar Cin Kofin Duniya ta 2007
a tseren matasa maza. Ya gama na 13 a cikin minti 24 da dakika 56. Ya gama da dakika 49 a bayan wanda ya lashe lambar zinare, Asbel Kiprop na Kenya. A Gasar Cin Kofin Duniya ta Sojoji da Filin 2009, Niyonkuru ya lashe lambar azurfa a tseren mita 10,000. Lokacinsa na mintuna 29 da dakika 37.14 ya kasance dakika 23.67 a bayan wanda ya lashe lambar zinare, Essa Ismail Rashed na Qatar. Niyonkuru ya kasance 4.97 seconds a gaban wanda ya lashe lambar tagulla, Tunisian El Akhdar Hachani. Niyonkuru ya lashe Auray-Vannes Rabin Marathon na 2015 a cikin sa'a daya, minti uku da dakika ashirin. A Wasannin Olympics na bazara na 2016, Niyonkuru ya fafata a tseren marathon na maza a ranar 21 ga Agusta 2016, amma bai gama tseren ba. A cikin 2017 ya yi gasa a tseren marathon na maza a Gasar Cin Kofin Duniya ta 2017, inda ya kasance na 71 a cikin 2: 42:27.