August joins from Red Consultancy, where she led and delivered campaigns for Huawei UK and McDonald's, among others.
She has previously worked at Iris, across integrated accounts for Samsung (Europe and global), Brita and Maplin, including Samsung's first live virtual reality gig, which helped it generate record sales for the Galaxy S7.
Mischief managing director Greg Jones said: "She's got fantastic experience across a wide variety of clients and campaigns and we're looking forward to seeing her work her magic on some of Mischief's biggest and best clients."
August added: "I have admired Mischief's work for a long time and am excited to work with an agency where creativity is at the heart of its practice, while still making a tangible difference for clients.
"I'm confident that my wealth of experience in the consumer tech and entertainment sectors can add to a company that already excels in those areas and I look forward to learning and working with the wider expertise within the Engine group too."