The team just made the big announcement on Wednesday ... saying the 27-year-old dominant defensive end will also serve as an ambassador for the organization.

"As a leader on and off the field, Myles has become a Cleveland icon and shares in our organization's commitment to being a transformative force for good across the region," Cavs owner Dan Gilbert said.

"We are honored to welcome this long-time friend of the team as our new partner and investor. Myles’ passion and commitment to the city he loves will allow us to reach new communities and continue to build the successful future of this franchise."

Garrett -- who's in the middle of a $125 million deal -- has been building his portfolio lately ... also investing in a Major League Pickleball team earlier this year.

The 2017 No. 1 overall pick has played in Cleveland his entire career ... racking up four Pro Bowls and two First-Team All-Pro selections.

He's also gotten pretty tight with the Cavs during his time in northeast Ohio ... even showing off his crazy dunking skills while hanging out with the squad at Summer League this past offseason.

"I have admired the Cavaliers organization’s hard work, tenacity and dedication to the community since my early days in Cleveland,” Garrett said. "To have the opportunity to join this impressive and purpose-filled franchise, under Dan’s leadership, is truly a dream come true."

The news comes just hours before the Cavs kick off their 2023-24 season against the Brooklyn Nets ... and the team will certainly hope Myles' dominance rubs off on Donovan Mitchell and Co.