Deputy President Cyril Ramaphosa's spokesperson Ronnie Mamoepa died in hospital at 23:15 on Saturday night, the Presidency announced shortly after midnight.
He was 56.
"The president and deputy president convey their sincere condolences to Mr Mamoepa's immediate and extended family, comrades, friends and colleagues," the statement read.
"This is a great loss to me personally, to The Presidency and government at large," said Ramaphosa.
"However, our thoughts are firstly and foremost with Ronnie's wife, Audrey, his children and his siblings. I offer my sincere condolences to Ronnie's relatives, friends, comrades and colleagues who have suffered the loss of someone who was much loved and respected across our country and beyond.
"We shall miss him greatly," Ramaphosa said.
The veteran spokesperson took ill a month ago and had to undergo surgery.
At the time, Ramaphosa visited him in hospital and wished him a speedy recovery.
Served with distinction
Mamoepa was "a former political prisoner and member of the Gauteng provincial legislature, was a highly regarded and accomplished public servant and veteran communicator who served the African National Congress and various departments in government with distinction", the Presidency said.
Mamoepa was a well known figure in media circles, having communicated the views and comments of various government ministers on topics as diverse as the Sudanese peace talks and the controversy over the Dalai Llama's planned visit many years ago.
He was also a spokesperson for Nkosazana Dlamini-Zuma when she was Home Affairs minister.
In her book Robben Island, Charlene Smith detailed Mamoepa's involvement as an ANC member during the struggle.
"Ronnie Mamoepa was a skinny kid who knew the slogans and songs by heart, and could raise his knees higher than most in the toyi-toyi," the book stated.
Smith said Mamoepa was convicted for terrorism in 1980, at just 18 years of age.
Condolences streamed in from politicians and the public on Saturday night as news spread of his passing. -- News24WireSuggest a correction