The case, involving the great-grandson of the third Baron Delamere, one of Kenya's first major white settlers more than a century ago, has attracted huge media attention.
The tall, besuited farmer showed no emotion as the sentence was read to a courtroom packed with foreign journalists, and relatives of both his and his victim's family.
Justice Muga Apondi told the court he had not taken into account the accused's offer to pay compensation to the dead man's family.
"There should not be one law for the rich and another for the poor," the judge said.
But he noted the accused had used his own car to take the man to hospital, after shooting him.
Protests in court
Mr Njoya had been hunting on Cholmondeley's 55,000-acre Soysambu ranch near Lake Naivasha in Kenya's Great Rift Valley, which teems with zebra, giraffes and other wildlife.
Serah Njoya has been left with four children, no job, and no husband
Correspondents say the case has touched on deep sensibilities in Kenya, where white people took vast swathes of the best agricultural land during British colonial rule until 1963, before the new Kenyan elite did exactly the same.
Acknowledging the tensions, Justice Apondi said: "This court understands the undercurrents, but I believe the executive is dealing with the issues of land and other inequalities," reported Reuters news agency.
He said the process had humbled the accused, so he wanted to deliver a light sentence, which is to start immediately, to let him reflect on his life.
After the sentence was read out, people started protesting in court and waving placards, one of which read: "The Butcher of Naivasha."
In 2005 Cholmondeley admitted shooting a Maasai ranger, but the case was dropped owing to insufficient evidence.
That decision provoked outrage and mass protests among the Maasai community.
The hedonistic lifestyle of the original Lord Delamere and other wealthy white settlers from central Kenya's "Happy Valley" set inspired a book and the 1987 film White Mischief.
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