PrettyGreen's brief includes supporting several launches, handling Brooks' press office and activating a campaign based on the brand's 'Run Happy' philosophy in 2020.
The agency will also operate a reactive newsroom alongside the Brooks influencer programme, with a 12-month calendar of activity.
Brooks previously worked with sports PR specialist Sponge Marketing.
Pretty Green said it will run a series of press events throughout this year to "demonstrate why Brooks is the go-to brand for runners' needs".
The agency's head of communications, Lucy Mart, said: "We are really excited to be working with Brooks – a respected brand that has truly innovated in running, with such a unique personality and point of view.
"PrettyGreen is passionate about sport, so to be able to become part of the Brooks team is a real win for us."
Brooks marketing manager of EMEA region north, Claire Butters, added: "PrettyGreen not only delivered a really strong response to the brief, but showed us a genuine love for the run and enthusiasm for our brand.
"When the creative idea comes from being on a run, then you know you're on to a good thing. We are excited to welcome them to the Brooks family and are looking forward to creating brilliant work with them."