The contract will start in July and the site will employ 1,200 people by the end of the year. The site will offer workers a range of shift patterns including part time, night shift and student friendly working hours.
All staff will be new to the Sheffield site, but a number of the employees will be existing Clipper staff members.
Steve Parkin, executive chairman of Clipper, said: “The new contract with Pretty Little Thing represents one of the company’s most significant contract wins and is demonstrative of our ability to deliver cost-effective solutions for retailers of any scale.
"We are delighted to have been awarded this contract with one of the fastest-growing online retailers, and look forward to working with the Pretty Little Thing team over the years ahead.”
Leeds-based Clipper said the new site will offer a fast-moving fashion, shoe and accessories ecommerce logistics operation involving inbound deliveries from a variety of UK-based and international suppliers over seven days a week.
It added that various forms of automation and mechanisation can be introduced over the next five years to facilitate the anticipated significant growth.
Mahmud Kamani and Carol Kane, joint CEOs of boohoo.com, said: “We are delighted to have successfully concluded our negotiations and to be entering into a contractual relationship with Clipper which we hope will be a long, successful and prosperous partnership for both parties."
Clipper also updated the market on current trading, saying that results for the year to April 30 is expected to be in line with the board's expectations, with continued growth in revenue, operating profit and net earnings.
Results for the year are expected to be announced in July.
Analysts at N+1 Singer said in a note: "The full year trading update highlights that trading in 2018 is expected to be in line with expectations, with continued growth in revenue, operating profit and net earnings. We are forecasting a record year of growth since IPO.
"The group has also announced a significant contract win with PrettyLittleThing.com, part of boohoo.com, to provide logistics services to PLT at and from a new 600,000 square foot site in Sheffield (current group square footage is just over 7 million).
"The new contract will commence in July 2018 and is said to be one of the company’s most significant contract wins to date."