Engle was named one of Major League Baseball's Scouts of the Year at last year's Winter Meetings, and is highly regarded for his work in international scouting.
With the Mariners, his international signings included Felix Hernandez, Erasmo Ramirez, Michael Pineda, Greg Halman, Carlos Peguero, Jose Lopez and Carlos Triunfel.
Engle told the club he would not be signing an extension when his current contract expires on Oct. 31.
"This was a very tough decision for me," Engle said in a statement released by the Mariners. "I have had a great time in Seattle and am proud to have served with so many fine people in the international department. I cannot thank the scouts and field personnel enough for their dedication and hard work.
"This was a most difficult decision to make, and I am planning to take the remainder of October to spend time with my family and assess my future and if I want to retire or remain in the game."
Engle also thanked Mariners CEO Howard Lincoln, president Chuck Armstrong and the three general managers he worked for -- Pat Gillick, Bill Bavasi and Jack Zduriencik -- "for allowing us to expand the international program since my arrival," as well as "the many people behind the scenes who are never recognized for their efforts and support."
Before coming to the Mariners in 2000, Engle, 65, was director of scouting with the Blue Jays when they drafted Roy Halladay, Chris Carpenter and Pat Hentgen, who, like Hernandez, all went on to win Cy Young Awards.
Engle originally was hired by the Mariners as a senior advisor to Gillick. He was promoted to VP of international operations in 2007 and estimated he spent about 175 days a year on the road in Latin American, Europe and Asia.
"I want to thank Bob for all of his efforts on behalf of the Mariners," Zduriencik said. "He, and the International group that he led, have done important work in identifying and signing players from around the world for the Mariners, including Felix Hernandez, Jose Lopez and many others that have made an impact on our Major League roster."