The makeovers will include public areas such as sun decks and lounges, and dining will be enhanced with the introduction of a new a la carte restaurant on each ship.
The news follows an earlier investment in the fleet in 2012 which saw all cabins on Thomson Dream and Celebration, together with some public areas, refurbished with contemporary designs.
Thomson Dream and Thomson Celebration will get a chic new sunbathing area whilst the food and beverage offering will be enhanced with the introduction of an Asian-themed a la carte restaurant, Kora La, offering Indian and Chinese cuisine on both ships.
Customers will also have a new food offering and décor at Terrace Grill on Thomson Dream. And a new look is planned for the former Argo Lounge and Oceans Bar on Dream when they reopen as The Explorers' Lounge & The Coffee Port and Tides Bar.
'Listening to our customers is at the heart of all our planning, which is why we are investing further in both Thomson Dream and Celebration to give passengers an even better experience on board,' said Helen Caron, managing director of Thomson Cruises.