Kim made the announcement Friday, saying a prisoner named Jeffrey Stringer would be walking free and reunited with his family soon after serving 22 years of a life sentence.

She posted this shot of Jeffrey's family members, who are clearly thrilled he's been granted a reduced sentence after more than 2 decades behind bars.

Sources connected to the case tell us Jeffrey was convicted for drug possession when he was 25, but because he had 2 drug priors ... he got life under the federal three-strikes law.

His attorney, Brittany K. Barnett -- who Kim credited for securing Jeffrey's release -- tells TMZ ... they went to court and successfully argued he should be released under the First Step Act, which President Trump signed into law last year.

Barnett, who co-founded the Buried Alive advocacy group for inmates like Jeffrey, says his "case epitomizes the catastrophic effect of 3 strikes." We're told he'll be released on Monday.

While Barnett did the lawyering, it appears Kim foot the bill. As she put it, "It gives me such joy to fund this life saving work."

As you know ... Kim's been dedicating much of her time to prison reform, helping Tennessee inmate Cyntoia Brown secure clemency, and playing a major role in freeing Alice Marie Johnson and Matthew Charles. She's even taken her cause to the Oval Office, meeting with President Trump ahead of Alice's release.

She's also studying hard to become a lawyer, and co-starring in her pal, Paris Hilton's music videos.

Busy woman.