Apple Inc.’s close-knit industrial design team is undergoing its most pronounced turnover in decades, marking a changing of the guard for the famed group that has defined the tech giant’s aesthetic and spearheaded the development of products including the iPhone.

Rico Zorkendorfer and Daniele De Iuliis, who together have more than 35 years of experience at Apple, decided to leave the company recently, people familiar with the departures said. Another member of the team with a decade of experience, Julian Hönig, plans to leave...