Khumalo‚ a sex worker‚ was beaten to death in Woodstock in 2013.
Judge Patricia Goliath delivered the verdict in the Western Cape Hight Court on Thursday.
Mthethwa was linked to the crime scene through CCTV footage which showed his black Porsche pull up next to Khumalo‚ before the driver exited the vehicle and attacked her.
Mthethwa argued that it was not him in the video‚ and called on “gait” experts to testify that the manner in which the attacker walked did not match his style of walking.
Dozens of activists had gathered outside the court awaiting the verdict.
Lesego Tlhwale from women's rights group Sex Workers Education and Advocacy Task Force (SWEAT)‚ said that a guilty verdict would mean “that sex workers lives don’t go unnoticed“.
“We are hoping for a positive verdict verdict [and] a life sentence. He beat Nokuphile without remorse.
“This has gone on for too long. Justice delayed is justice denied‚” Tlhwale said.
Mthethwa’s large scale photographs of South Africans have been exhibited worldwide at venues such as the Museum of Modern Art in New York and the International Centre of Photography.