In January, the 17-year-old boy was sentenced to eight years in prison for murdering his 19-year-old sister in Landskrona, south Sweden.
A district court judged that "honour motives" were behind the murder, but the boy, who was 16 at the time of the killing, is demanding to be freed.
The case will now be re-tried in the Malmö Court of Appeals.
The boy's lawyer, Urban Jansson, has criticized his client's long detention period, telling news agency TT that it does not befit Sweden as a country governed by the rule of law.
The 19-year-old woman was found dead in her apartment in Landskrona on April 23rd last year. She had multiple stab wounds to her body.
She had previously lived in a foster home and had recently celebrated her 19th birthday in the apartment.
She had returned to Sweden after fleeing a forced marriage in Iraq.
Representatives of the Malmö-based organization Tänk om, which works to stop honour-related crimes, told local media that the woman had been in touch with them for one year since returning to Sweden and that she slept with a knife under her pillow for fear of reprisals over her escape.
They claimed local authorities had ignored their warnings that the woman was under threat and needed protection.
Police arrested the woman’s 16-year-old brother after finding him outside the apartment, tabloid Aftonbladet reported at the time.
The trial starts Tuesday.
TT/The Local/nr Follow The Local on Twitter