PrettyLittleThing is a fast growing, international online retail brand, which will complement boohoo's own inclusive and innovative brand.
The boohoo board expects the transaction to extend the group's presence in the UK and internationally and enhance its strong growth trajectory.
Peter Williams, chairman of boohoo, said: "PrettyLittleThing was always going to be a natural fit with boohoo.
"Umar and his team are to be congratulated for creating a fantastic brand, which complements boohoo's own inclusive and innovative brand, and we are delighted to add this fast growing, international business to the group.
"We believe this is an excellent opportunity to extend the group's overall customer appeal through two distinct, complementary brands while further enhancing the group's strong growth trajectory.
"We look forward to building on PrettyLittleThing's success and we welcome Umar and his team to the group."