As part of the £55million deal, the troubled department store will relaunch as an online-only operation later this year.
Debenhams announced its business would be wound down in December 2020, in a move affecting 124 shops and 12,000 jobs.
A few weeks ago, Debenhams then confirmed six stores, including its flagship Oxford Street shop, will permanently close.
The retailer’s stores are currently shut due to lockdown rules, but shoppers can still purchase goods on its website.
Once Debenhams stores reopen after lockdown, the retailer will continue to clear stock in its shops while the website will be operated by Boohoo.
The closing down sale will then continue in stores for several weeks, after which shops will close permanently, the retailer’s administrator said.
Boohoo said Debenhams was then expected to relaunch on Boohoo’s web platform by late spring or early summer.
Debenhams’ own fashion brands will also be absorbed into Boohoo’s current portfolio and sold via the website.
Meanwhile, Debenhams’ 12,000 workers are set to lose their jobs after the winding down period as the deal doesn’t safeguard jobs.
Debenhams has already cut 6,500 jobs since May after falling into administration for the second time in April.
The majority of Debenhams’ current employees in the UK are currently being paid under the government’s furlough scheme.
The business was set to be liquidated after JDSports pulled out of bids to save the troubled department store chain.
The collapse came after Debenhams’ sales in the six months to October plunged to £323million versus billions in its heyday.
The deal comes as online retailer Asos has bid to buy Topshop, Topman and Miss Selfridge brands from Arcadia Group, which is the biggest operator of concessions in Debenhams stores.
Sir Philip Green’s retail empire collapsed into administration in November, putting 13,000 jobs at risk.
Boohoo said the Debenhams deal represents a “fantastic opportunity” to target new customers and launch into the beauty, sports and homewares market for the first time.
Boohoo has previously bought a number of well-known high street brands out of administration, turning them into online-only operations, including Oasis, Coast and Karen Millen.
Geoff Rowley, joint administrator and partner of FRP Advisory, added: “We are pleased to have secured the future for this great brand, and to have created the opportunity for a new Debenhams-branded business to emerge in a different shape beyond the pandemic.
“I expect that the agreement with Boohoo may provide some job opportunities but we regret that this outcome does not safeguard the jobs of Debenhams’ employees beyond the winding down period.”