In a statement on Monday, the iconic company's board of directors thanked Mr King for his "extraordinary contribution".
"In what will be more than six years at the end of his tenure, John will have delivered a remarkable turn-around in the positioning and performance of the business."
Without going into details, the board said it understood Mr King's desire to be with his family in the United States "as their health circumstances demand".
Myer was struggling with more than $100 million in net debt, unprofitable stores and poor customer satisfaction when Mr King joined.
Its most recent financial statements were its best in nearly a decade - a $65m half-year profit for the 26 weeks to January 28, a cash balance of $267.3m, and a special dividend for shareholders.
Under Mr King's leadership Myer also reduced its overall space by 11.1 per cent while expanding its ecommerce offerings and loyalty program.
Roy Morgan in February ranked Myer as Australia's sixth most-trusted brand in Australia, just behind Kmart.
"I am proud of what we have achieved so far with lots more to do, so it will be a busy year ahead," Mr King said.
The board said the long lead time between the announcement and his retirement would allow it plenty of time to search for a replacement.
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