Folic acid is to be added to non-wholemeal wheat flour across the UK to help reduce neural tube defects in babies by around 20%, or 200 cases a year.
The decision follows a consultation in 2019 and is based on evidence of successful fortification in Australia, New Zealand, and Canada.
NHS recommendations already urge women who are pregnant or planning a pregnancy to take a daily 400 microgram folic acid supplement.
Fortification is designed to help protect unplanned pregnancies. The additional cost is estimated to be minimal and the addition of folic acid follows the current calcium, iron, niacin, and thiamine fortification.
Kate Steele, CEO of Shine, the spina bifida and hydrocephalus charity, said she was "delighted" at the announcement.
"Mandatory fortification of flour with folic acid will improve public health for so many, now and in the future," she said.
"In its simplest terms, the step will reduce the numbers of families who face the devastating news that their baby has anencephaly and will not survive. It will also prevent some babies being affected by spina bifida, which can result in complex physical impairments and poor health. This is truly a momentous day."