PARIS — François Pinault’s decades-long battle to place his contemporary art collection here took a leap forward this week when the Japanese architect Tadao Ando unveiled his design to turn a historic rotunda in central Paris into a circular private museum housing the luxury magnate’s collection.

Mr. Pinault, who is one of the world’s top collectors and also owns Christie’s, said the museum would open in early 2019 after a renovation of the Bourse de Commerce, a former grain exchange that was later used as a stock market, and more recently to house the Chamber of Commerce. The building is modeled on the Pantheon and situated between the Louvre and the Pompidou Center, France’s pre-eminent contemporary art museum.

“In creating this new museum, I am writing the next chapter of my cultural project, whose goal is to share my passion for contemporary art with as broad an audience as possible,” Mr. Pinault said at a news conference at the building, which has a glass dome and frescoes representing trade.

Mr. Ando plans to build a circular structure with three levels of galleries inside the round building, which is bound by strict historic preservation norms. It will have 32,000 square feet of exhibition space and an underground auditorium. The museum, which will only showcase contemporary art — including pieces from Mr. Pinault’s collection of more than 3,000 works — will be renovated and run by his family’s company, after a Bourse renovation expected to cost around 108 million euros, or $121 million.