Art.com is one of the largest online sellers of art and wall decor globally, Walmart said. A person familiar with the deal said the size of this acquisition is similar to Walmart's other recent deals and that Art.com recently was bringing in more than $300 million in sales annually.

The retailer has been building a collection of e-commerce companies in categories ranging from clothing to lingerie since its roughly $3 billion acquisition of Jet.com in 2016. Those brands now include ModCloth, Moosejaw, Bonobos, Eloquii and Bare Necessities. The strategy helps Walmart target a younger audience that isn't accustomed to going to its stores, as it rivals Amazon online.

Walmart plans to buy Art.com, adding another digital brand to its portfolio and bolstering its home decor business.

Eventually, items from Art.com will be sold on Walmart.com, Jet.com and Hayneedle.com, Walmart said. It will continue to run Art.com as a standalone website and wouldn't comment on its plans to add merchandise from Art.com to Walmart stores. The website has roughly 2 million designs to chose from, and growing, according to Walmart.

Walmart has already started adding items from some of its acquired brands to its website. Outdoor gear company Moosejaw, for example, now has its own shop on Walmart.com. Walmart also landed a deal with Lord & Taylor to sell apparel from the department store chain on Walmart.com, again going after a more high-end and younger customer, something it hasn't been able to do with its traditional brands.

It also aspires to do more with technology, and buying Art.com should help with that.

"As we think about the future right now, art will be one area where we will leverage augmented reality," Anthony Soohoo, the senior vice president of Walmart's online home business in the U.S., told CNBC. He said 25 percent of Art.com's customers currently use a feature on the platform called ArtView, where shoppers can see what a piece of art looks like on their walls before they buy. Walmart will be able to "leverage that expertise" about augmented reality in other categories of its business moving forward, Soohoo said.

The deal is expected to close early next year.

Walmart could one day own upwards of 40 digitally native brands, according to the head of its U.S. e-commerce business, Marc Lore.

"Just four brands aren't going to do it, but imagine 40," Lore told investors earlier this fall. "The idea is to buy and build."

Walmart has also started building its own online brands, one being Allswell, which launched earlier this year and sells bedding and mattresses. It runs on its own website, AllswellHome.com.

CORRECTION: This story was corrected to say Art.com was recently bringing in more than $300 million in sales annually, according to a person familiar with Walmart's acquisition. A prior version of this story misstated that amount.