[10] With former champions Kenenisa Bekele and Zersenay Tadese not competing at the 2010 IAAF World Cross Country Championships, Tanui was suggested as a tentative favourite for the competition.

[12] He failed to carry over his strong domestic form to the world stage, but the 19-year-old still managed to reach the top ten in his first attempt at the senior level, finishing eighth and helping Kenya to the team gold.

[13][14] Seventh place at the 2011 Kenyan trials meant that he was not selected for the world event,[15] but a dispute between Leonard Komon and Athletics Kenya saw Tanui drafted in as a late replacement.

[16] He went on to finish the 2011 IAAF World Cross Country Championships as his nation's best performer by taking the silver medal, two seconds behind race winner Imane Merga.

[19] At the beginning of 2012, he beat Geoffrey Kipsang in a sprint finish to win the men's race at the Cross Internacional Juan Muguerza and was runner-up at the Trofeo Alasport.