Holler will be responsible for expanding the brand by repositioning it in the market, with the aim of attracting new customers as well as retaining existing ones.
The agency, which is part of Leo Burnett Group, will act as Pretty Green's lead shop alongside Neighbour, the branding and design specialist.
Holler will lead below-the-line digital communications for the brand as well as deal with strategy and communications planning for above-the-line media buys. The agency will also support brand developments, including the promotion of new season lines.
The first work to be undertaken by Holler will be a campaign to launch Pretty Green's sunglasses range.
The campaign will include an interactive event involving Gallagher, the former Oasis frontman, and fans of the brand.