Nolubabalo 'Babsie' Nobanda will serve 15 years in a Thai prison after she was caught with 600g of cocaine woven into her dreadlocks.
International Relations spokesman Clayson Monyela said Nobanda was also fined R250,000.
"Initially, she was given a 30-year sentence but that term was reduced because she was co-operative with the authorities. They reduced the jail sentence by half," said Monyela.
He said the department was in contact with Nobanda's family in South Africa.
"Through our embassy in Thailand we will continue to visit her [in jail] and give her necessary support," he added.
Nobanda, 23, from Grahamstown, in the Eastern Cape, was arrested at the Bangkok International Airport in December for trying to smuggle cocaine from Brazil to Thailand.
Police found 1.5kg of cocaine with an estimated street value of US150,000 (about R1.2 million) in her dreadlocks.
She admitted to smuggling the drugs and said she had been hired to deliver the cocaine to a customer at a hotel in Bangkok.
She has been imprisoned since then.
Nobanda was represented by a Bangkok state lawyer.
According to Grahamstown advocate, Ntsiki Sandi – who is her uncle – Nobanda narrowly escaped serving 30 years behind bars after the presiding judge reduced her sentence by half due to her personal circumstances, which were found to be extenuating.
She failed in her bid to serve out her sentence in a South African prison, close to her family.
Speaking to the Daily Dispatch shortly after sentencing, Sandi said that theoretically his niece could have received the death penalty.
Janice Bronwyn Linden, also from South Africa, received the death penalty for drug smuggling by the Chinese government at around the time of Nobanda’s arrest.
“I cannot say that we are happy with the sentence, no time in prison is good, but it could have been worse; the family had prepared themselves for worse,” Sandi said.