"Our Ancestors are watching and protecting us now more than ever!" he wrote. "This is for Our Future Kids kids. We are the generation that will change this!"
The post accompanied a blackout picture, a sign of support for the black community across social media Tuesday.
It's been a continuation of protests that have taken place nationwide following the death of George Floyd, who was killed while in police custody in Minneapolis on May 25.
Irving's previous post was about Ahmaud Arbery, an African American man who was killed in Georgia in February by two armed white men who followed and confronted him because they believed he was a suspect in a string of break-ins in the area.
The All-Star point guard was also seen taking part in a protest Tuesday.
The 28-year-old is in his first season with the Brooklyn Nets after signing a four-year deal last summer, although a shoulder injury limited him to just 20 games in 2019-20 before being ruled out for the rest of the season.