The deal will see Sundial operate as a standalone business within Unilever and continue to be run by founder, Richelieu Dennis, who started the business in 1991 after moving to the US from Liberia.
Dennis was inspired by his grandmother, who sold handmade soaps and other products in her native Sierra Leone.
The company’s site states: "Sundial’s products are inclusive, serving all people to address underserved issues such as hyperpigmentation, dark spots and the special needs of textured hair, as well as consumer demands for efficacious natural products."
The agreement will see Unilever and Sundial create the $50m (£37.6m) New Voices Fund, which will be used to empower female women of colour entrepreneurs. Unilever said it intended to double the size of the fund by attracting investments from other interested parties.
Kees Kruythoff, president of Unilever North America, said: "The Sundial team has built differentiated and on-trend premium brands serving multicultural and millennial consumers that enhance our existing portfolio."
Dennis commented: "I’ve always wanted Sundial Brands to be an inspiration to other minority-owned companies of how a business against all odds can achieve excellence, have significant social impact in our communities and be successful on a world stage.
"I am excited Sundial and Unilever have created this partnership, rooted in a purpose-driven ethos, that represents an incredible opportunity to take our Community Commerce economic empowerment and impact model to another level."
The acquisition comes after Unilever Ventures last month made an investment in "cruelty-free" start-up Beauty Bakerie, which has been cited by bloggers and media brands as one of the best beauty brands for people of colour.