The operator runs trains from Paris, Brussels and Amsterdam to London St Pancras International.
The firm issued a statement which read: “If you have a valid visa to enter the UK, along with your Ukrainian passport, please speak to a member of the Eurostar team at Paris Nord, Brussels-Midi, Lille Europe or Amsterdam Central stations, and they will issue a ticket for travel to London.”
Transport union TSSA welcomed the decision.
General secretary Manuel Cortes said: “Our union warmly welcomes Eurostar’s offer of free travel for Ukrainian nationals heading to Britain and we praise the company for this practical act of support and solidarity with the people of Ukraine.
“Our members working at Eurostar are proud of their employer’s approach and will support Ukrainian passengers in their time of need.”
State rail operators in several European countries such as Poland, Germany and France are also offering free travel to Ukrainians.