Williams is one of the top-ranked players in his class ... and has earned a massive following on social media with 3.2 million followers on Instagram alone.

Now that the NCAA and most states allow college athletes to make money off their name, image and likeness, Mikey has followed up by becoming the very first high school athlete to sign a NIL deal -- teaming up with Excel Sports, an agency that works with superstar athletes like Tiger Woods, Nikola Jokic and Clayton Kershaw.

The deal will help the Vertical Academy junior guard secure endorsements and sponsorships WAY before he makes it to the college level ... and Excel VP Matt Davis tells ESPN the partnership "will generate millions of dollars for this young man."

Williams spoke about the monumental moment ... saying, "The NIL rules provide a new opportunity for someone like me who that has put in so much energy and effort into building a community."

"I am excited to be the first high school athlete to make this move. I love to hoop and I love engaging with my fans and look forward to continuing to share my journey with everyone."

FYI -- there are no laws in North Carolina that prevent high school athletes from making NIL deals, so it seems like Williams will not hit any roadblocks on the way to makin' serious coin.

It's a sign of what's to come for young athletes all over the country ... and ya gotta wonder if Williams' fellow Class of 2023 prospect Bronny James is next.