Eurostar passengers will be required to cover their faces from Monday 4 May or risk being refused travel.
The rail company said the rule for travellers to wear face coverings is in line with guidelines from the French and Belgian governments.
Any type of face covering is allowed "as long as it effectively covers your nose and mouth", a statement said.
It comes after Prime Minister Boris Johnson said face coverings "will be useful" as the UK eases lockdown.
Mr Johnson's comments followed a Scottish government recommendation for people to cover their faces when in shops and on public transport.