Eurostar is to add an eleventh daily service in each direction on the London to Brussels route from December 14.
The rail operator said the new service – which operates Monday to Friday only – is being introduced to meet growing demand from travellers.
Passenger numbers on the route have increased by 30% since November 2007.
The additional service also means Eurostar will reintroduce its Ashford to Brussels route.
Eurostar director of communications Simon Montague said: “The eleventh daily service will give travellers more options when planning a trip to the Belgian capital or a connecting journey to a destination elsewhere in Belgium, the Netherlands or Germany.”
Tickets goes on sale from August 16.