Sun Dawu described enduring “misery beyond words” during months-long police interrogations that forced what he said was a false confession.

Sun Dawu, a rural tycoon and outspoken critic of the Chinese Communist Party, was sentenced to 18 years in prison Wednesday, the latest in a string of harsh punishments meted out by China against business leaders.

The 67-year-old Mr. Sun had been detained in November after a land dispute between his company, Dawu Agricultural and Animal Husbandry Group, and a neighboring state-owned farm. Prosecuted in a trial closed to the public alongside 19 family members and employees, Mr. Sun was convicted of a range of crimes, including organizing people to attack state agencies, obstructing public affairs, and provoking quarrels.

Long a thorn in the side of Beijing, Mr. Sun was a frequent and loud critic of Chinese government policies, from its early handling of Covid-19 to local government cover-ups over a 2019 outbreak of African swine fever that killed thousands of his pigs. He was also a businessman who cultivated an image of generosity. As his agricultural empire grew he created a town around his holdings and provided services, like hospital care, to employees.

The harsh sentence comes amid broader efforts by the Chinese leader, Xi Jinping, to muzzle outspoken business leaders and bring the private sector to heel. Under Mr. Xi, a growing number of tycoons have been punished and a barrage of new rules has laid low corporate Goliaths in the technology and education industries. Stocks for some of China’s best-known companies, like Tencent and Didi, have sagged, while an antimonopoly investigation into Alibaba led to a $2.8 billion fine.