"I know I have given cricket my all, it's been my life for 20 years. There's not much more I could give," he said at a hastily called press conference at the WACA ground in Perth ahead of Friday's match.
Ponting, who turns 38 next month, has failed in three innings against the Proteas during draws in Brisbane and Adelaide and pressure has been building on the veteran ahead of the crucial series decider.
He will continue to play for Tasmania in the domestic competition this summer.
Perth will be a fitting place for Ponting to end a remarkable international career: it is where he debuted against Sri Lanka in 1995.
By playing on Friday, he will equal Steve Waugh's mark of 168 Test matches, the most in the history of Australian cricket.
After being made captain in 2004, right-hander Ponting went on to become one of the country's greatest cricketers, winning more Tests as skipper (48) than any other Australian.
The Tasmanian has 13 366 Test runs to his name, including 41 centuries at an average of 52.21, with only Indian legend Sachin Tendulkar scoring more. But he said he knew it was time to call it a day.
"Over the last couple of weeks my level of performance hasn't been good enough," said Ponting, who had already been dumped from the one-day and Twenty20 international squads.
"My passion and love for the game hasn't changed but at the end of the day [the decision] was based on my results.
"In this series so far they have not been up to the level required of batsmen and players in the Australian team," he added.
"I'm glad I have got the opportunity to finish on my terms."
Ponting insisted the decision was entirely his own and he had not been pushed by selectors. The normally stoic batsman, affectionately known as Punter, said he was highly emotional when he told his teammates.
"I tried to say a lot but I didn't get much out," he said. "They'd never seen me emotional before, but I was this morning."
Michael Clarke, the current captain, was close to tears following Ponting into the press conference, saying he would be sorely missed and the announcement took him by surprise.
"I didn't have a feeling it was coming," Clarke said of his friend and mentor.
"Ricky spoke to me after Adelaide and obviously made his decision over the last few days.
The boys [in the team] are obviously hurting right now. He's been an amazing player for a long time."
Clarke said later he attempted to persuade Ponting to change his mind. "I certainly tried to," he told Channel Nine.
"Like all of the players in the change room we would still like him to be there."
Clarke said the announcement would only fire up the side to win the third Test, where the number one ranking in Test cricket will be on the line.
"It will only give us more inspiration," he added.
In a statement, Cricket Australia chief James Sutherland described Ponting as one of the best players ever to pad up for his country.
"Ricky has had an extraordinary career and has made an extraordinary contribution, including through the example he has set for other elite players and through the excitement he has given fans, young and old," he said.
"I think his record until he retired as captain was outstanding but my respect for him since then has actually increased, seeing firsthand how he stepped back to become a total team player."
Ponting said he would take time to decide what to do in his Test retirement, but Sutherland said he hoped he would remain connected to the game "in an official capacity". – Sapa-AFP