Telstra chief financial officer and board member John Stanhope will leave the company at the end of calendar 2011.
Mr Stanhope is retiring, Telstra said in a statement.
Telstra chief executive David Thodey said the telco had started looking for a replacement.
Mr Stanhope, who joined Telstra in 1967, said he would still have some work to do before stepping down on December 30, with a shareholder vote on the deal with the federal government on the national broadband network.
"I look forward to continuing to play a significant role in the coming months as we seek shareholder approval for Telstra's participation in the national broadband network," Mr Stanhope said.
Telstra shareholders will vote on the deal at the company's annual general meeting set down for October 18.
"We look forward to him continuing to play a critical role as we seek shareholder approval for Telstra's participation in the national broadband network," Mr Thodey said.
"John's contribution to the company for more than 40 years has been enormous."