The additional train service has started in time for a major new Van Gogh and the Sunflowers exhibition in the Dutch capital, which runs from 21 June to 1 September at the Van Gogh Museum.
To mark the occasion, Eurostar commissioned costume designer Kate Tabor to create a gown made of fresh sunflowers.
The service from St Pancras to Rotterdam and Amsterdam was first launched in April 2018 after years of delays.
Mike Cooper, Eurostar’s chief executive, said: “With environmentally responsible travel rising up the consumer agenda, we’re boosting capacity and offering more flexibility with a third daily service.”
The journey time from St Pancras to Rotterdam is three hours 13 minutes and to Amsterdam three hours 52 minutes.