IndiaCoco will initially launch online. It is due to open its first store next year.
Social media will be used to drive brand awareness and customer champions will be recruited to develop the upcoming autumn/winter collection.
Harper was marketing director at Mamas & Papas for five years before departing in November and has previously been head of online marketing at Sainsbury’s and head of marketing at Ocado.
She is co-founding IndiaCoco alongside finance director Lee Williams, who used to be divisional finance director at Morrisons and has also held senior finance roles at Comet, Woolworths and Tesco.
Harper and Williams are parents to daughters Coco and India, who inspired the brand name.
IndiaCoco will aim to champion the best of British childrenswear brands and has already secured partnerships with independent product brands including ‘No Added Sugar’, ‘Ilovegorgeous’ and organic brand Frugi.
The retailer will aim products at active kids from zero to eight years and claims packaging will be "simple, stylish and environmentally friendly".
Harper said: "Customer service is paramount to the success of IndiaCoco and we will deliver the service we know our customers deserve.
"We are focused on executing a super easy, quick and simple website, a seamless 360 [degree] brand experience and fast delivery, all beautifully packed and presented directly to the customer.
"We also want parents to choose IndiaCoco because of our outstanding customer service and the warmth, passion and the commitment that shines through everything we do."
Follow Matthew Chapman at @mattchapmanUK