JOHANNESBURG -- South Africa's highest court has dismissed Oscar Pistorius' appeal of his murder conviction, a lawyer said Thursday, signalling that the former track star's long legal battle since he killed girlfriend Reeva Steenkamp may be drawing to a close.

The ruling by the constitutional Court clears the way for a judge to sentence the double-amputee runner for murder at a hearing scheduled for April 18.

"We'll proceed to the sentencing," defence lawyer Andrew Fawcett said.

Pistorius, who killed Steenkamp in 2013, had appealed to the constitutional Court, saying another court erred when it overturned a manslaughter conviction and declared the Olympic athlete guilty of murder.

Pistorius spent one year of a five-year sentence in jail for the lesser offence. He is currently under house arrest, staying at his uncle's mansion in Pretoria.

The minimum sentence for murder in South Africa is 15 years, though a judge can reduce that sentence for what the law describes as exceptional circumstances.

Pistorius shot Steenkamp through the door of a toilet cubicle in his home early on Valentine's Day 2013. Prosecutors said he killed her after an argument; Pistorius said he killed her by mistake, thinking there was an intruder in the house.

Pistorius, a multiple Paralympic champion, became the first amputee to run at the Olympics and the able-bodied world championships. He was known as "Blade Runner" for his carbon-fibre running blades.