Judge Thokozile Masipa announced that Pistorius will serve a sentence of six years in prison.
In her decision, Masipa said Pistorius was a "good candidate for rehabilitation", as he had proven during the 10 months he spent in prison before being eligible for parole under house arrest. The defense team countered by asking Masipa to sentence Pistorius-who is a double amputee and made history in 2012 by becoming the first Paralympian to compete in the Olympics-to no jail time and argued for a sentence that included charity work instead.
The lawyer for Pistorius later said he would not appeal against the sentence.
Ms Steenkamp's parents, Barry and June, sat quietly on the other side of the packed courtroom.
After the verdict was read, Pistorius, 29, who was dressed in a dark suit and white shirt quietly hugged his sister before he was whisked off to Khosi Mampuru prison in Pretoria to start serving his sentence.
On Valentine's Day 2013, Pistorius fired four times through a bathroom door, hitting Steenkamp, three times.
Pistorius, who pleaded not guilty at his trial in 2014, has always denied killing Steenkamp in a rage, saying he was trying to protect her.
"The life of the accused shall also never be the same".
Advocate Mannie Witz says Masipa weighed up all the facts.
The murder case involving a former Olympic sprinter that's lasted almost three years is finally over.
She said that the athlete would have to serve a custodial sentence because his conviction had been upgraded from manslaughter to murder.
"Public opinion may be loud and persistent, but it can play no role in the decision of this court", said Judge Masipa.
He had his legs amputated below the knee as a baby.
"We are very disappointed... from five years that we fought against, and now it is six, what is that?"
Women's rights groups say Pistorius has received preferential treatment by the justice system compared to non-whites and those without his wealth or worldwide celebrity status.
On Feb. 14, 2013, Pistorius fatally shot Steenkamp at his home.
A double-amputee, Pistorius won several gold medals at the Paralympics and also competed at 2012 London Olympics, drawing global attention by running on his carbon-fiber prosthetics.