The win gave Heather Knight’s England a 10-6 win in the multi-format series.
England got off to a rocky start chasing 154, when India dismissed Tammy Beaumont early for just 11 runs, with Deepti Sharma dismissing the dangerous opener LBW in the 4th over.
However, a 112-run stand between Wyatt and Nat Sciver (42 off 36 balls) powered the host to a comfortable win.
Earlier, India elected to bat first on what looked like a batter-friendly surface in Chelmsford.
It came down to the captain and vice captain as Harmanpreet Kaur and Smriti Mandhana put together a 68-run stand for the third wicket.
Chief Scores
India Women: 153/6 in 20 overs (Smriti Mandhana 70, Harmanpreet Kaur 36, Sophie Ecclestone 3/35)
England Women: 154/2 in 18.4 overs (Danni Wyatt 89 n.o, Nat Sciver 42).
(Agencies)