The Caribbean side claimed the top spot after Sri Lanka, who had largely occupied the top spot since they won the World Twenty20 in 2014, were whitewashed by New Zealand in their two-match series on Sunday.
New Zealand completed the sweep following an easy nine-wicket victory in Auckland. They completed the victory in 10 overs
West Indies have 118.36 rating points, and are now marginally ahead of both Sri Lanka and Australia ahead of the World Cup in India in March.
West Indies have played eight matches since the end of the World Twenty20 in April 2014 and won four of them, including a world record chase against South Africa in January 2015.
Sri Lanka had started the two-match series against New Zealand with a seven-point lead. Losing it 0-2 meant they were yet to win a Twenty20 series since becoming World Twenty20 champions (although they beat England in a one-off match in May 2014) and were pushed off their No. 1 slot.