Kane Williamson of New Zealand celebrates his century during day four of the second Test cricket match between New Zealand and Sri Lanka at Seddon Park in Hamilton on December 21, 2015. AFP PHOTO / MICHAEL BRADLEY / AFP / MICHAEL BRADLEY (Photo credit should read MICHAEL BRADLEY/AFP/Getty Images)

Kiwi batsman Kane Williamson is now officially the world's No.1 Test batsman.

Williamson's century, which helped guide New Zealand to a 2-0 series win over Sri Lanka, was enough to help propel him above Joe Root and AB de Villiers to the No.1 ranking.

Williamson has been in brilliant touch this year, scoring 1,172 Test runs at an average of 90.