SEATTLE — After nearly 40 years as a leader of Starbucks Corp., Howard Schultz is stepping down as executive chairman and member of the board, effective June 26.

Mr. Schultz, who now will become Starbucks’ chairman emeritus, transitioned from chief executive officer to executive chairman of Starbucks on April 3, 2017. At that time, he shifted his focus to innovation, design and development of Starbucks Roastery stores and Reserve bar initiatives around the world, expansion of the Starbucks Reserve retail store format and the company’s social impact initiatives.

Mr. Schultz also served as Starbucks’ c.e.o. from 1987 to 2000, eventually stepping down to focus on the company’s global strategy. He remained chairman of the board until 2008, when he reclaimed the top position to revitalize the company.

“Those of us who were around in (the economic downturn of) 2007 and 2008, we allowed a disease to enter the halls and the company," Mr. Schultz said in an address to hundreds of Starbucks partners on the afternoon of June 4. "And that was hubris. And we allowed ourselves to be caught up in growth. We lost our discipline, we lost our belief in our core purpose. How easy it was to lose, (yet) how hard it was to get back.”

During Mr. Schultz’s time as chairman and c.e.o. of Starbucks, the chain grew from 11 stores to more than 28,000 stores in 77 countries. Under his leadership, Starbucks said, the company delivered a 21,000% gain in stock price value since its initial public offering in 1992.

“I set out to build a company that my father, a blue-collar worker and World War II veteran, never had a chance to work for,” Mr. Schultz said in a letter addressed to past and present Starbucks partners. “Together we’ve done that, and so much more, by balancing profitability and social conscience, compassion and rigor, and love and responsibility.”

Mr. Schultz’s relationship with Starbucks began in 1981 when he entered the first Starbucks store in Seattle’s Pike Place Market. The next year, he was appointed director of operations and marketing, eventually purchasing Starbucks with the support of local investors and dedicating his career to expanding the chain.

“There are no words to fully express our gratitude to Howard for the extraordinary company he has built,” said Kevin Johnson, c.e.o. and member of the board of directors. “He’s helped Starbucks earn the respect of millions around the world by always being true to a higher calling and always being bold in creating a better future. He’s taught all of us that it’s possible to be a very different kind of public company. That must, and will, continue on my watch.”

Mr. Schultz will still oversee the opening of the Starbucks Reserve Roastery in Milan on Sept. 6 and the New York Roastery in late October. After that, Mr. Schultz said he plans to write a book about Starbucks’ social impact work as well as explore other opportunities.

“I’ll be thinking about a range of options for myself, from philanthropy to public service, but I’m a long way from knowing what the future holds,” Mr. Schultz said in the memo.

Mr. Schultz owns 37.8 million shares of Starbucks, worth about $2.17 billion.

Effective upon Mr. Schultz’s retirement, Myron E. (Mike) Ullman — former c.e.o. of JCPenney and Macy’s — will become chair of the board, and Mellody Hobson — president at Ariel Investments — will become vice-chair of the board.