From 1 September its staple own-label yoghurt, dairy ice cream, milk, cream, Cheddar and butter will be sourced entirely from British dairy farms.
Only own-label dairy products with specific geographic origins such as Canadian Cheddar, Brittany Butter and Wexford Cheddar will continue to be sourced from outside Britain.
The retailer said its new strategy would boost British dairy industry confidence against a backdrop of dwindling numbers of dairy farms and farmers.
Waitrose and its suppliers had worked together to make the 100% British move possible, the retailer said. Its own-label yoghurt and dairy ice cream suppliers are the most recent to have guaranteed British-sourced products.
The supermarket was confident it could maintain 100%-British supply even after meeting corporate targets to double the business by 2016, agricultural manager Duncan Sinclair added.
"In the past, every time the business has expanded, it hasn't had to compromise standards," he said.
Waitrose dairy farmers at an event this week also claimed they would be able to increase supply.
"We have been expanding production slightly faster than Waitrose has been expanding sales," said farmer David Homer.
The initiative was welcomed by the NFU's chief dairy adviser, Hayley Campbell-Gibbons.
"It is refreshing to see a retailer that has adopted a can-do attitude and there is no reason why other retailers can't do the same in sourcing own-label products," she said.
Along with its milk processor, Dairy Crest, Waitrose pays one of the highest farmgate milk prices in the industry to its dedicated farmers. In June, that stood at 27.29 pence per litre.
On-farm investment has included improvements to housing, bedding areas and milking parlours, as well as measures to prepare for tighter waste management legislation.