The human rights campaigner visited Williams in San Quentin prison on Saturday (19NOV05) and was brought to tears by the plight of the former Crips gang leader - who was convicted of four murders 25 years ago.
She says, "I appeal to Governor Schwarzenegger. You could grant him clemency; change death to life imprisonment without parole.
"We must do the right thing. Executing Williams is not only shutting down the possibility of rehabilitation that exists in all of us, but it would be, as well, a great injustice to execute someone who is innocent."
Civil rights leader Jesse Jackson, who accompanied Jagger, adds, "The evidence, at best, is shoddy. His reputation as a gang leader was on trial, not the actual evidence of the murders."
Williams is scheduled to be put to death on 13 December (05) and Schwarzenegger has admitted he's "dreading" making the final decision.