Though its constitution still describes members as “vanguard fighters of the Chinese working class imbued with communist consciousness,” the party has veered away from its communist roots and welcomed private entrepreneurs since 2001. Some of the richest men in China are party members, including Wang Jianlin of the Dalian Wanda Group, a property and entertainment conglomerate, and Xu Jiayin of the Evergrande Group, a property developer.

It is unclear when Mr. Ma joined the party or how much he pays in dues. The party sets dues at 2 percent of monthly salary for higher-income members.

The star power of the Chinese entrepreneur class has dimmed since Xi Jinping became the country’s top leader in 2012. Under Mr. Xi, the Communist Party plays a bigger role in not only Chinese politics but also the economy and everyday life. Any entity with more than three party members is required to set up a party cell. Some three-quarters of private enterprises, or 1.9 million, had done so in 2017, according to official data.

Companies say they face much greater pressure to set up the cells than in the past. Even some of the coolest start-ups in tech-savvy Beijing have designated party-building spaces.

The disclosure of Mr. Ma’s membership reflects the thinking that the party controls the economy and society, said Guo Yuhua, a sociology professor at Tsinghua University in Beijing and a critic of the party.

“It’s going backward from the Deng Xiaoping era, when the party advocated the separation of the party and the government,” she said, referring to the party leader who ultimately governed China during its early years of reform in the 1970s and ’80s.

The disclosure also drew attention because Mr. Ma had in the past tried to keep his distance from the government. When asked at public appearances how he managed government relations, he often said, “Fall in love with the government, but don’t get married.”