Amnesty International is opposed to the death sentence handed to prison beauty queen Ruth Kamande.
Kamande was convicted on Wednesday after she was found guilty of killing her boyfriend Farid Mohammed in 2015 by stabbing him 22 times.
The organisation wants the death sentence to be commuted and for 24-year-old Kamande to be rehabilitated.
"Amnesty International opposes the death penalty in all cases without exception regardless of the nature of the crime, the characteristics of the offender, or the method used by the state to kill the prisoner," it said in a statement on Friday.
Executive Director Irungu Houghton said that the death penalty was a violation of the right to life.
"It is the ultimate cruel, inhuman and degrading punishment," he said.
Irungu further added the organisation was concerned that the country continued to use the 'outdated' mode of punishment.
"This sentence is a blow to Kenya’s progressive record in commuting death sentences to terms of imprisonment."
Irungu claimed that there wasn't any credible evidence that the death penalty deters crime any better than other lawful punishments.
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Judge Jessie Lessit, when giving her ruling, said Farid was killed in a calculated manner.
She further held that Kamande did not appear to have suffered any anguish, hence deserved a death penalty.
The judge further said it was a lesson to young people not to kill their partners but instead walk away and forgive when a relationship breaks down.
Though the Supreme Court has ruled that the death sentence is not mandatory, judges have discretion to impose it in cases of grievous crimes.
No executions have been carried out in Kenya since 1987 when Kenya Air Force senior private official Hezekiah Ochuka and Pancras Oteyo Okumu were hanged for treason.
In 2016, President Uhuru Kenyatta signed commutation documents turning all death sentences into life jail terms.
Invoking the Power of Mercy provided by Article 133 of the Constitution, Uhuru also signed a pardon warrant and released 102 long-term convicts.
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