The 26-year-old raced in 68 grands prix with Swiss-based Sauber from 2022 to 2024 and has been managed by Cadillac team principal Graeme Lowdon.
US-owned Cadillac, the 11th team on the grid with experienced Finn Valtteri Bottas and Mexican Sergio Perez as race drivers, will be using Ferrari engines when they debut in Australia in March.
Cadillac also have American former IndyCar driver Colton Herta, who will compete in F2 this year, as test driver.
Shanghai-born Zhou, who was teammate to Bottas at Sauber, is the only Chinese driver to have raced in Formula 1 and the Liberty Media-owned sport sees the country of more than a billion people as an important growth area.
"I have worked with both Graeme and Valtteri for many years in various capacities, so joining the team feels like rejoining family," he said.