LaQuan Smith, whose body-hugging fashions have graced stars like Rihanna and Cardi B, is ready to dress millions of 20-somethings.

This week, ASOS, an online retailer catering to shoppers in their 20s, plans to announce a collaboration with Mr. Smith, a 29-year-old designer with a following among women of color. The ASOS Design x LaQuan Smith collection of women’s, men’s and unisex clothes and accessories, debuts on ASOS’s site in October.