CMW will be responsible for repositioning the business to focus communications on the brand’s proposition of chef prepared and calorie controlled meals.
Activity will launch across TV, print and digital and social media. The campaign will launch over the summer in the UK before rolling out to other European markets.
Liz Wilson, chief executive, CMW, said: "This is a fantastic opportunity for the agency.
"Diet Chef is an exciting and brave client operating in a hugely crowded sector.
"While the category is obsessed with the end result, weight loss, research shows us that half the dieting audience are more concerned about the quality and taste of food so this represents a massive opportunity for us to own this area."
Liz Dale, marketing director, Diet Chef, said: "CMW's pitch provided us with exactly what we're looking for in an agency.
"They showed a deep insight into our business and consumers and provided some truly integrated creative thinking."
In January Diet Chef appointed Mindshare to its £2m media planning and buying account. The relationship remains unaffected by CMW's appointment.