Mischief was appointed following a non-competitive pitch and will start working on the account in April. The account was previously held by Wild Card.
Mischief will handle consumer campaigns and a creative press office, focusing on the launch of new single serve puds.
Gü’s founder, James Averdieck, came up with the idea for a chocolate dessert brand when he was working in Belgium and launched three products in 2003.
Gü’s head of brand Chris Heyn said: "We want to take Gü to the next level to really surprise and delight consumers and make our puds the go-to choice for those wanting an indulgent treat. Mischief’s innovative thinking will help us create disruptive and impactful campaigns that make people sit up and take notice."
The account will be led by Mischief PR creative director Damon Statt and associate director Charlotte Dolman.