Xolile Mngeni, 25, was found guilty of premeditated murder at the Western Cape High Court.
He was also convicted of robbery with aggravating circumstances and illegal possession of a firearm and ammunition.
He was acquitted of kidnapping the 28-year-old newlywed.
Anni Dewani's husband, Bristol businessman Shrien Dewani, is currently being held at a secure mental health unit in the city while he fights extradition to South Africa to face trail over the kiling.
He denies ordering the murder on Novemeber 13, 2010.
The South African authorities want the 32-year-old extradited to stand trial for murder, but two High Court judges ordered earlier this year that he was not in a fit mental state to go back.
Taxi driver Zola Tongo, 31, from Cape Town, has already admitted his part in the killing and was jailed for 18 years as part of a plea bargain.
One of the gunmen, Mziwamadoda Qwabe, has also admitted his part in the crime.