The six-figure contract was previously held by Mischief, and was won by Cirkle following a competitive pitch.
The brief was awarded last week and Cirkle hopes to begin activity this week.
Noble Foods, the owner of the happy egg co, is the UK's largest producer of free-range eggs, according to Cirkle.
Cirkle told PRWeek in a statement that it would "focus on recruiting own label free-range egg consumers to the brand by driving differentiation for the happy egg co and demonstrating how it sets the gold standard in hen welfare".
Managing director Ruth Allchurch said the agency would "leverage the brand’s personality through an integrated mix of innovative consumer, social and trade initiatives that will create genuine cut-through in a highly commoditised category".
Rob Newell, marketing director at the happy egg co, said: "The integrated campaign will ride on the positive momentum around eggs in terms of animal welfare, health benefits and consumer desire for provenance and transparency - while showing consumers why the brand is worth paying a little more for. We look forward to the team unlocking influence and advocacy to drive brand saliency and importantly, penetration."