The model praised her friend on Instagram Stories for testifying in Johnny Depp's legal battle with Amber Heard.
Campbell, 52, tweeted, "YES WAGON TELL IT!! @ katemossagency"
Campbell's words were accompanied by a screengrab of a court article in which Moss denied Heard's claim that Depp pushed her down stairs during their '90s romance.
Moss testified in Depp's $50 million defamation lawsuit against Heard. The Fairfax County Circuit Court trial is in its sixth and final week.
Moss said he was never pushed, kicked, or thrown down stairs.
Moss told jurors she fell down a flight of stairs at Jamaica's GoldenEye Resort on a rainy night.
Johnny left before me, and it was raining. As she left, she slipped down the stairs and hurt her back.
"I screamed because I was hurt and unsure what happened. "[Depp] ran back to help me, carried me to my room, and got me medical attention."