Fat Joe's rubbing elbows with some of the top politicians in the country ... specifically Vice President Kamala Harris -- and he's sharing his solutions for some of the country's greatest issues, too.

The outspoken rapper met up with the VP on Friday afternoon and led a panel regarding criminal justice reform featuring Kentucky Governor Andy Beshear and White House Director of the Office of Public Engagement Steve Benjamin.

The convo -- which featured a few other prominent criminal justice advocates and three recipients of marijuana-related pardons -- lasted about an hour and featured lots of personal anecdotes from those pardoned.

We're told Fat Joe expressed his gratitude for how his journey through hip hop had landed him in a close relationship with the vice president -- who he apparently met through his healthcare reform group Power To The Patients.

BTW ... we're told Joe actually sat down for a private conversation with Kamala where the two talked about healthcare price transparency and other issues close to Joe's heart.

Harris isn't the only exec who Joe's spoken to in recent days ... the Bronx-bred rapper also caught up with President Joe Biden himself -- following the Prez's SOTU address, which took some shots at Donald Trump.

Sources told us members of both parties wanted a piece of Fat Joe after he dapped up Biden ... with reps on both sides of the aisle rushing to the man for an autograph.

Fat Joe's been on the advocacy grind for a while now ... and we even talked to him about Power to the Patients on "TMZ Live" back in January.