There are no other legal options available for Oscar Pistorius after his request was dismissed to appeal against his 13-year jail term, said the National Prosecuting Authority (NPA).
The former Paralympic athlete, 31, had asked the Constitutional Court to review the jail term, which was increased to 13 years in November.
But the court ruling released on Monday said that "the application for leave to appeal is dismissed" as it was not a constitutional matter.
The ruling was dated March 28.
"This is the end of the road. There are no other legal options available," NPA spokesperson Luvuyo Mfaku told AFP.
He welcomed the ruling, which ended the long legal battle over Pistorius killing his girlfriend in 2013.
Tania Koen, the Steenkamp's family lawyer, said that Reeva's parents had "always had faith in the justice system" and had no further comment to make.
"June and Barry have been focusing their time and energy in the Reeva Rebecca Steenkamp Foundation which was established in her memory," Koen said.
Pistorius shot dead Reeva Steenkamp in the early hours of Valentine's Day in 2013 when he fired four times through the locked door of his bedroom toilet, later saying that he thought she was an intruder.
He was originally convicted of culpable homicide - the equivalent of manslaughter - in 2014, but his conviction was upgraded to murder on appeal.
Pistorius also tried to take the murder conviction to the Constitutional Court, but it also refused to hear the matter.
His legal team and state prosecutors have fought through the courts over the length of his sentence. The year before he killed Steenkamp, Pistorius became the first double-amputee to race at the Olympics when he competed at the London 2012 games.
Previously a role model for disabled people worldwide, his trial generated international headlines.
In a television interview, he said he believed an intruder was in the house and "instant fear" drove him to grab his gun and walk on his stumps towards the bathroom before opening fire.
It is unclear when Pistorius, who is detained in prison outside the capital Pretoria, could be eligible for parole.