The same judge originally convicted him of manslaughter after months of hearings, but a higher court changed that to murder in December.
Barring an appeal, it will be the final chapter of a saga that began on that fateful February morning in 2013 — when Pistorius fired four bullets through his bathroom door.
There’s only one person who will ever know precisely what transpired in Pistorius’ home that day.
The prosecution said Pistorius had a violent streak, and that he murdered his lover after a late-night argument.
But the defense has always maintained that the amputee track star mistook Steenkamp for an intruder and feared for his life when he shot through the door.
Despite a seven-month trial, much remains in question about what happened at 4 a.m. that morning, leaving stunned fans wondering how their hero turned into a killer.
While the opposing sides offer different versions of what happened, one thing is certain: Pistorius will not be a free man for a long time.
And it’s not the first time he’s going to prison in Steenkamp’s killing.
Guilty of manslaughter
After a nearly 50-day trial stretched over seven months, Pistorius was found guilty of culpable homicide (much like manslaughter) in September 2014.
But the Supreme Court of Appeals overturned the verdict last December. The appeals judge said Pistorius should have known that firing his gun would have killed whoever was behind the door, regardless of who he thought it was. It found Pistorius guilty of murder.
The minimum prison sentence for murder in South Africa is 15 years, and the prosecution has called for no less. But the defense tried to secure a shorter sentence for Pistorius by arguing that his disability and emotional state were mitigating factors.
In giving him six years, the judge cited mitigating circumstances for the lesser punishment, saying Pistorius is a good candidate for rehabilitation. She added that Steenkamp’s parents have forgiven him.
Defense: Pistorius feared for his life
In dramatic scenes during his sentencing hearing in June, Pistorius hobbled across the court
without his prosthetic legs, weeping as defense attorney Barry Roux argued that the former Olympian and Paralympic gold medalist was a broken man who deserved leniency.
“He suffers from an anxiety disorder. We know that … when he was on his stumps, his balance was seriously compromised, and without anything he won’t be able to defend himself,” Roux said.
Pistorius was not wearing his prostheses at the time of the shooting. Roux painted a picture of a fearful man on his stumps, trying to protect a loved one. He said Pistorius never intended to kill Steenkamp, and that he had tried to save her life.
“He was anxious, he was frightened. … He was suffering from anxiety disorder, and that’s not gone,” Roux said. “This must all be seen in context of his disability.”
“The accused can never resume his career,” Roux said. “The accused has punished himself and will punish himself for the rest of his life far more than any court of law can punish him.”
Steenkamps: Pistorius must pay for his crime
Nel said it was the victim’s father was the “broken man,” not Pistorius.
Weeping and trembling on the stand, he told the court that he still speaks to his daughter every day and thinks of her “every morning, afternoon and night. I think about her all the time.”
“I don’t wish that on any human being, finding out what happened. It devastated us,” Barry Steenkamp said. “I ended up having a stroke and so many things since then have happened to me.”
The father said his wife, June, had forgiven Pistorius, but that the former Olympic and Paralympic sprinter must still pay the price for his crime.
“You have to understand that forgiveness doesn’t exonerate you from what you did,” he said.
CNN’s David McKenzie and Laura Perez-Maestro contributed to this report.