Armstrong will work through Jan. 31 and the team said a search for his replacement will begin immediately.
"Thirty years ago, my family and I were given a wonderful opportunity to move to the Seattle area and become associated with the Seattle Mariners," Armstrong said. "We quickly grew to love this community and this team. Through all the good times and the not-so-good times on the field since 1984, the goal always has been to win the World Series. My only regret is that the entire region wasn't able to enjoy a parade through the city to celebrate a world championship together."
Armstrong said his decision was fueled by a desire to spend more time with family.
"After much thought and reflection, it is now time for me to retire and enjoy as much time as possible with my wife, Susan, and our family," he said. "The recent deaths of several good friends have really had an impact on me and helped crystallize my decision. This was a very difficult, very personal decision, but I know in my heart that it's time to turn the page and move to the next chapter of my life.
"Thanks to our outstanding ownership, the franchise is stable and will remain the Northwest's team, playing in Safeco Field, a great ballpark and great example of a successful public-private partnership. The team is in good hands and positioned for future success. I am thankful for this important part in my life and I will always bleed Mariners Blue. Susan and I plan to continue to live here and remain involved in many community events and causes."
Armstrong has worked as team president under two ownership groups. The Kentucky native originally served as team president and chief operating officer for Argyros from 1983-89, then was let go after the club was sold to Smulyan.
Armstrong remained in the Seattle area and was interim athletic director at the University of Washington in 1991 before returning to the Mariners in '92 after working as a consultant during the sale from Smulyan to the current Nintendo ownership group.
Armstrong has remained team president the past 21 years. He has been active during that time both in Seattle and in Major League Baseball, where he has served on the board of directors of MLB Enterprises, Inc., the 14-member Commissioner's Special Committee for On-Field Matters, MLB International Committee and the Commissioner's Ticketing Review Committee.
MLB Commissioner Bud Selig described Armstrong as "a great baseball man" and wished him well in his retirement.
"Chuck was one of the key leaders who secured the national pastime's future in the Pacific Northwest, guiding the Mariners as they became a model franchise in a wonderful ballpark," Selig said. "His knowledge and experience on both the baseball and business sides was an asset to our entire sport in numerous ways, including on my Special Committee for On-Field Matters and our International Committee, and he always kept the best interests of our game in mind.
"I and Chuck's many friends throughout the game will miss him both personally and professionally. On behalf of Major League Baseball, I wish Chuck, his wife, Susan, and their family all the best, and I thank him for his many contributions to the game he loves."
Armstrong received his undergraduate degree from Purdue University in 1964 and graduated from Stanford University's law school in 1967 before serving three years of active duty in the U.S. Navy. He then worked for a Los Angeles law firm, was president of a furniture manufacturing company and then president and CEO of a real estate investment company owned by Argyros in California.
When Argyros purchased the Mariners, he brought Armstrong to Seattle to help run the franchise, and he and his wife have made their home in the Northwest since.
"When the Baseball Club of Seattle purchased the franchise in 1992, it was clear that Chuck Armstrong was uniquely qualified to lead the organization," said Mariners CEO Howard Lincoln. "Since Day 1, he has given his heart and soul to Mariners baseball. He sincerely cares about the game of baseball, this organization, this city and this region. On behalf of ownership and everyone who has worked here for the past 30 years, I thank Chuck for his tremendous contributions. We wish him all the best in retirement with Susan and his family."