Rev Williams arrived at Kutbul Kai near the river Tlawng in Mizoram from Syhlet (now in Bangladesh) and visited Aizawl where he preached Christianity to some Mizos.
Earlier, the Presbyterian Church Mizoram Synod used to observed January 11, the anniversary of the arrival of two Welsh missionaries - Rev. J.H. Lorraine and Rev. F.W. Savidge in 1894 as the Missionary Day.
After the conference of the Mizoram Synod held in 2012 and after a thorough research, March 15, the arrival of Rev. William Williams has been observed as the Missionary Day.