"I am delighted that I now have my good name and livelihood back," Mamabolo said on Wednesday.
"I rely on running to support my family."
Mamabolo tested positive for methylhexaneamine last season, shortly after he became the first South African in seven years to win the Comrades Marathon.
His B-sample confirmed the presence of the banned stimulant.
Werksmans Attorneys, which handled Mamabolo's case on a pro bono basis, said the athlete had been found not guilty on Tuesday in a 60-page judgement after facing a committee appointed by the SA Institute for Drug-Free Sport.
As many as 15 irregularities were found in the testing process.
"We are certain this is the right result for him and for sport," said Werksmans Attorneys director David Hertz.
In an unprecedented move in South African athletics, Mamabolo turned to the courts and was allowed to return to competitive running in February in order to earn an income and prepare for this year's Comrades Marathon, pending the outcome of the hearing.
He subsequently won a half-marathon in Limpopo in February and finished second in a 21km race in Mokopane.
He struggled, however, at the Two Oceans 56km ultra-marathon in Cape Town in March, trailing home more than 26 minutes behind race winner David Gatebe.
Mamabolo confirmed he would return to defend his Comrades title in this year's 89km race, an "up" run between Pietermaritzburg and Durban on June 2. – Sapa