State prosecutors had requested this sentence - without parole - for 22-year-old Johannes Kana.
South Africa has one of the highest rates of sexual violence in the world.
'Shocking and inhumane'
The BBC's Nomsa Maseko at the court in Swellendam, 220km (136 miles) from Cape Town, says Kana's uncle clapped his hands and laughed as the judge announced the sentence.
"This is a joke," he said, adding that the system was unjust.
Many of those attending the trial feel justice has been served, our correspondent says.
But some in the community have raised questions about whether Kana was the only person involved in the attack as Ms Booysen told police before she died that there were several assailants, our reporter says.
|This is the 2nd demonstration in Africa this week against Rape. This is good.|
At the time President Jacob Zuma described the attack as "shocking, cruel and most inhumane".
He called for courts to impose the "harshest sentences" for sexual crimes. This is good too!
During the trial, doctors who treated Ms Booysen described her horrific injuries - one said they were the worst injuries she had ever seen.
Just before she died, she said in hospital that five or six men had been involved in the attack.
But state prosecutors say that at the time she was intoxicated, in pain and under heavy medication so she may have been confused.
Three suspects were initially arrested but only Kana stood trial.
He confessed to raping Ms Booysen but denied killing her.
Meanwhile, charges against four of five men accused of kidnapping, raping and killing two young girls in Diepsloot, a shanty town north of Johannesburg, were withdrawn at the Pretoria Magistrate's Court on Friday.
The state prosecutor said evidence showed the men were not in Diepsloot at the time of the crime last month. A fifth man remains in custody and the case was postponed until 27 November to allow for further investigation.
South African police figures show that 64,000 incidents of rape were reported last year. That's how many were reported; how many actually occurred was likely several times that number.
Police say that a child is raped every three minutes in the country. Since it probably takes more than 3 minutes to rape a child, one can assume that child-rape is constantly occurring in South Africa.
Please pray my 3:15 PM prayer and pray that this is the beginning of a revolution against sexual violence against children in South Africa. The demonstration, President Zuma's words, and the harsh sentence are a good start. It's a pity it had to take the horror endured by Ms Booysen to initiate action.