The 34-year-old, who won his 100th cap at the 2011 World Cup, has played in all three of Australia's Tests this year and was named in the starting line-up for Saturday's third and final Test against Wales.
Sharpe said in February he would be retiring at the end of his 15th Super Rugby season in August but has had a change of heart and will play on in the replacement for the Tri-Nations, which will also feature Argentina.
"Sharpey's indicated that he's willing and keen to play on into the Rugby Championship so that's good news for the group," coach Robbie Deans said.
"He's vastly experienced, he's been in this arena for a long time "It is a big decision for Sharpey, he'd made plans around his life beyond the game and he's had to put them on hold. That's a significant commitment from him. I don't think it's an indefinite deferment, though."
Sharpe made his international debut against France in 2002 and has played 104 times for his country, including in the 2003 World Cup final loss to England. He captained the Wallabies twice.
Australia are likely to be without one of their second row options, captain James Horwill, for the rest of the season because of a hamstring injury and, Sharpe apart, their stocks of experienced locks are low.
Sitaleki Timani will play only his third Test when he partners Sharpe on Saturday at the Sydney Football Stadium as Australia look to seal a 3-0 win against the Six Nations champions.
Rob Simmons, who played in the second row for the first two Tests against Wales and for much of last year, drops to the bench as part of a strategy to blood new locks.
"The moment is coming when Sharpey is not going to be available to us so we've got to prepare for that," Deans added.
"We want to give Sita some exposure, bring him on. Simmo's had a big year, played a lot of rugby. The sooner we can bring Sita on the better it will be for us."
Dan Vickerman is another experienced Australian lock but he was likely to call time on his career because of an ongoing problem caused by a stress fracture in his leg, Deans said.
The South African born 33-year-old returned from three years studying in England to play in his third World Cup last year but now looks unlikely to add to his 63 caps.
"I understand his leg's giving him a fair amount of grief day to day so I think he's probably at the point where he's conceded his playing career is over," "But I haven't had formal notification of that and with Dan, you never know. He's already shown he can work through adversity."
Deans said Sharpe, a fierce competitor unmistakable for his shaven head and staring eyes, would not be continuing on to Australia's tour of Europe in November.
"Yeah, that won't be happening is the initial indication," he laughed.