The move ends Thorntons' relationship with the previous incumbent, PHD Compass, but it retains Miles Calcraft Briginshaw Duffy as its creative agency.
Thorntons ran a £2 million TV campaign last Christmas through MCBD. The spot, which starred Robson Green, used the line: "Thorntons. Perfection in confection. It aimed to positioned chocolate as the ultimate Christmas present.
Thorntons has managed to turn around its business following a period of instability by refocusing on its strategy and its product range.
This restructure, which included the scrapping of 15 per cent of product lines, seems to have been a success - last month it unveiled its best sales figures for the past five years, with increased profits.
The company is planning to expand the number of stores it has from the existing total of 395 with 180 franchise outlets and is now planning to add 20 more franchises each year for the next two years.
Thorntons is also leveraging its brand name and has entered into deals with supermarkets to allow them to sell its branded products. It has entered a 12-month exclusive deal to sell its chocolate bars through Tesco.
The head of advertising and design at Thorntons, Richard Burgess, said: "Starcom Motive showed a clear and unique understanding of our requirements and demonstrated a real passion and commitment to maximising value for our investment. We are all looking forward to working with it."