The CEO will depart the company on March 31, 2014, with former Optus CEO Paul O'Sullivan briefly stepping back into the CEO role in Australia until a replacement has been found.
O'Sullivan said Russell had mentioned to him "several months ago" that he was looking to move onto other challenges after repositioning the company. O'Sullivan paid tribute to Russell's work at the company in his two years in the role.
"Kevin joined Optus just over two years ago, and has provided strong leadership in repositioning the company. Several months ago, Kevin told me that he wished to move on to other challenges on completion of this phase, after ensuring an orderly transition that embeds the strategic transformation he has led," he said in a statement.
"Kevin has worked with our management team to roll out a number of positive changes to Optus. We have a strong leadership team in place to deliver our goal of becoming Australia's most-loved service brand, and with the recent transformation of Optus' mobile network and customer experience, we are well placed for the year ahead."
It is understood that O'Sullivan had only briefed his senior executive team on his decision to leave the company this morning.
Russell's arrival at Optus two years ago heralded a change in the way the company operated, and the plans on offer to customers. On returning to Australia after five years abroad, he said the telecommunications market in Australia had deteriorated. He instituted a number of new plans, and ceased charging large excess fees to customers who go over their monthly data or call limits.
Earlier this month, Optus reported that for the three months to the end of December 2013, Optus shed 64,000 customers and recorded a AU$98 million decline in mobile revenue, but a 41.4 percent jump in year-on-year profit.
The outgoing CEO of Optus rival Vodafone, Bill Morrow, paid tribute to Russell.
"I admire Kevin, he's a straight-up guy, a professional of high integrity. I have no doubt he will be missed at Optus."