The move comes as all sorts of art-world players rethink the traditional ways art gets traded online, from former Christie’s auctioneer Loïc Gouzer’s Fair Warning auction app to the proliferation of digital platforms selling NFT artworks. Even as the art world’s attention increasingly pivots back to in-person art events including fairs, online sales of luxury goods remain robust and some top industry dealmakers see a bigger market opportunity in finding fresh ways to sell art to collectors accustomed to shopping for art online.

“Collectors go to gatekeepers because they need pricing info, but we want to put collectors in control,” said Mr. Chinn, Sotheby’s former chief operating officer. Late last year, he teamed up with artificial-intelligence experts and former auction specialists like George O’Dell to buy and retool Live Auction Art, then an auction-tracking data site. The new owners have now equipped the site, renamed LiveArt, with machine-learning technology so it can analyze auction data and give users free, real-time estimates of their collection’s likely market value. The key to success will be convincing collectors that LiveArt’s pricing and provenance services are as reliable as those collectors would get from the auction houses.

The architect behind the tech is Boris Pevzner, a graduate of MIT known for creating and selling several companies that use AI-driven algorithms, including one that resolves freight-shipping issues and another that manages art collections, Collectrium, that he sold to Christie’s in 2015.

Starting later this month, LiveArt will add the marketplace component to double as an online platform for private art sales. People can upload artworks and specify any details they want shared or kept from potential buyers, including their own identities. Once listed, an artificial-intelligence bot on the site will help them sift offers or field questions from potential buyers—like bots on retailer sites already do—as well as mediate deal terms so both parties remain discreet, if they choose. Once under contract, the seller will be asked to ship the work to the company’s clearinghouse in Delaware, where conservators and former auction specialists will check its condition and vet provenance before sending it on to its buyer, Mr. Chinn said.

He added that LiveArt has hired a team of provenance researchers, including some from Phillips, to vet work and if there are provenance disputes between buyers and sellers, the site will offer mediation. (LiveArt only charges buyers a flat 10% fee for any sales versus the big auction houses which can charge more than 20%.)

Christie’s and Sotheby’s didn’t immediately comment on Mr. Chinn’s new venture.

New York art adviser Alex Glauber, who isn’t involved with the venture, said the matchmaking element of a peer-to-peer digital marketplace could “solve a practical problem” for collectors who want to sell middle-market pieces without paying steeper fees to an auction house or wrangling a gallery to promote their consignments ahead of the gallery’s own inventory or artists.

Mr. Glauber said he plans to upload a few pieces to test the experience before he suggests it to his clients. He said the challenge will lie in persuading a “critical mass” of sellers, who typically prize discretion, to reveal the art they’ve got in storage. “Even with all the security assurances, some people may be reluctant to push their pieces online,” he said. “It’s going to take some convincing.”

David Rogath, a Connecticut collector who owns pieces by David Hockney and René Magritte, said he also has no ties to the venture but said he has bought and sold plenty of art through Mr. Chinn during his tenure at Sotheby’s, so he’s intrigued by the platform. “I have things I want to sell and things I don’t want anyone outside my family to know I own, and Adam understands discretion is key,” Mr. Rogath said.

Mr. Rogath said he used LiveArt’s pricing tool to test the values for several works he’s owned over the years and said he found them accurate. Mr. Rogath also said the site appears to smooth out some “speed bumps” that have historically dissuaded top collectors from brokering major sales to each other, including the logistics of hiring third parties to research and vouchsafe a piece’s condition and authenticity. If a platform can take over those real-world hassles, he said, “For a collector, there’s an allure to cutting out the middle man.”

Write to Kelly Crow at kelly.crow@wsj.com