CHI presented against Mustoes and Fallon to secure the business. The pitch was handled by ISBA.
The brief covers the company's entire portfolio, including Tate & Lyle Sugar, Lyle's Golden Syrup and a mass-market, low-calorie product to be launched in September.
The agency will also work with the company on developing a strategy to tackle concerns about rising obesity.
The low-calorie sugar market is becoming increasingly competitive. In September last year, Silver Spoon, the market leader, launched its reduced-calorie variant, Silver Spoon Light, with a campaign through Walsh Trott Chick Smith.
Tate & Lyle is the second- largest brand in the UK's £268 million sugar market, with a market value of £71 million. The Lyle brand is worth a further £10 million.
Sarah Gold, the managing director at CHI, said: "It will be a challenging year for us, given sugar is likely to be the next item on the obesity agenda, but one we will relish."
Julia Clark, Tate & Lyle's marketing manager, oversaw the pitch. She said: "CHI got under the skin of our brand."