The Bold is Beautiful event will take place over a 4.5-mile route, which starts and ends at Cavendish Square.
Participants will commence the walk wearing minimal make-up, and will collect Benefit products at checkpoints along the walk, as well as receive 'touch ups' to their lips, eyes and brows.
To take part, a minimum donation of £10 must be made to one of the aforementioned Bold is Beautiful charities. Refuge is a domestic violence charity, meanwhile Look Good Feel Better helps women fight the visible signs of cancer.
The event, which launched in 2015, is headed up by Benefit ambassador Denise Van Outen.
In addition to the march, the Bold is Beautiful campaign will see Benefit donate all profits from its brow waxing to the two charities throughout the month of May.
Customers who purchase a brow wax at Benefit will also receive a free Gimme Brow eyebrow gel over the period.
Ian Marshall and Gail Bojarski, managing directors at Benefit said: "Benefit has been transforming brows and empowering women since 1976 and this year we’re taking our feel-good approach to beauty to new levels.
"Bold is Beautiful raises more awareness and of course, much needed funds for our charity partners, Refuge and LGFB. We are looking forward to donating the proceeds from our brow wax services during the month of May and using this to help create bigger, bolder and more beautiful lives for women and girls across the UK."
Van Outen added: "I am truly proud to be a part of this year’s Bold is Beautiful campaign. Our incredible UK charity partners, Look Good Feel Better and Refuge, support women and children undergoing serious times of adversity and help them to regain a sense of self and wellbeing.
"I’ve had the pleasure of meeting some of these women and have been humbled by their experiences. I urge everyone to get involved as we attempt to raise as much money as possible for this amazing cause!"
The brand is also hosting a pop-up celebrating its best-selling products at a boat on the Thames all this summer.