A lawyer for Oscar Pistorius says South Africa's highest court has dismissed the former track star's appeal of his murder conviction.

The ruling by the constitutional Court on Thursday in Johannesburg clears the way for a judge to sentence Pistorius for murder at a hearing scheduled for April 18.

In December, the double-amputee Olympian was convicted of murdering his girlfriend Reeva Steenkamp by a South African appeals court.

The Supreme Court of Appeal overturned a lower court's conviction on the less serious charge of manslaughter, adding another twist to a case that riveted people around the world because of its gripping saga of a celebrity athlete's plunge from grace by his own hand.

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 is currently under house arrest.

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-fiber running blades.

Pistorius, 29, 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.

Steenkamp, a model who appeared in a television reality show, had planned to give a speech touching on domestic abuse and family relationships at a school on the day she died. In a tweet the day before she died, she wrote: "What do you have up your sleeve for your love tomorrow???"