Mackenzie and his co-accused will be given their sentence on November 6.
He was arrested in 2023 after police received a tip-off, and weeks later authorities began uncovering bodies in shallow graves in the Shakahola Forest near the coast in southeastern Kenya.
Prosecutors say Mackenzie and his Good News International Church organised a Christian doomsday sect in which they ordered followers to starve themselves and their children to death to go to heaven before the world ended.
Mackenzie denied murder charges, saying he did not force the victims to starve, but the court rejected that argument.
In total, more than 400 bodies have been recovered from the Shakahola Forest.
Many were severely decomposed, with only 26 bodies able to be identified.
Monday's judgment covered 191 deaths while investigations into the other deaths are ongoing.
Justice Diana Kavedza Mochache said in a hearing lasting more than eight hours that in some cases children were isolated and denied food while their parents watched.
Mackenzie was in court, wearing a striped polo shirt and red trousers, sitting alongside his wife who is one of the co-accused.
When his name was read out by the judge he stood silently, staring into space.
Family members of some of those who died in the forest gathered to hear the judgment at Mombasa High Court.
Francis Wanje, 62, lost eight family members including two grandchildren to the cult.
Speaking before the verdict, he told Reuters: "It has been really a heavy thing (for) us as a family, and it has really taken us very far in terms of psychological problems, ... I was hoping for this particular day."
The Shakahola tragedy has gripped Kenya since the discovery of mass graves in the coastal forest more than three years ago.
It raised questions over how Mackenzie was able to continue to operate despite having been on the radar of the authorities since 2017 when his premises were searched by police.
In 2019, authorities shut down Mackenzie's church and he relocated to the Shakahola Forest, police said.
The case has also led to calls for tougher oversight of churches and other religious organisations in a country where religious faith plays a prominent role in public life.
Kenyan President William Ruto said in 2023 that government agencies should have been able to prevent the deaths.
He said he took responsibility as president.
People with direct knowledge of the cult's activities told Reuters that Mackenzie planned the mass starvation in three phases: first children, then women and young men, and finally the remaining men.
A former taxi driver, Mackenzie forbade cult members from sending their children to school and from going to hospital when they were ill, branding such institutions as Satanic, some of his followers told Reuters for a 2023 article.
Cult members lived in makeshift homes of polythene sheeting and thatch that Mackenzie divided into areas with biblical names like Jerusalem and Judea.
The plight of his followers began to emerge in mid-March 2023, when a local man told police that his brother and wife had starved their children to death in the forest on Mackenzie's orders.
Mackenzie was arrested but released on bail, after which relatives say he brought forward the date on which he told his followers the world would end.
Police arrested him again in April 2023 and started combing through the forest more systematically and began exhuming mass graves.
Mackenzie faces other charges over the forest deaths including terrorism-related ones, which he has denied.
Prosecutors say while he was in detention he also directed the deaths of 52 people in Kwa Binzaro village, which lies about 30km from Shakahola.
Mackenzie has pleaded not guilty in that case.
