Mehari Wodaje, 46, who was doing time for second-degree murder, was found unresponsive in his cell Thursday.
Guards performed CPR and an ambulance was called but Wodaje was declared dead in hospital.
He had been in the prison since Nov. 5, 2007.
His trial was told Wodaje was in love with Tiruye Yizengaw but was distraught that she had married another man and strangled her to death with a telephone cord.
The trial was told tests indicated Wodaje had sex with her shortly before she was killed. He then tried to kill himself afterward.
The Crown initially charged Wodaje with first-degree murder on the basis the crime had been committed during a sexual assault, but the defence argued the sex was consensual and that Yizengaw was unhappy at having to marry a childhood friend.
The defence also argued the pair had made a suicide pact but that Yizengaw asked Wodaje to kill her first.
However, the Crown presented evidence that Yizengaw was nervous about Wodaje and only reluctantly agreed to meet with him the day she died.
Yizengaw was a member of the Ethiopian Orthodox Church while Wodaje was in his second year of nursing studies.