The Get Lucky hitmaker became close to the singer when he collaborated with her on the star's new album Bangerz.
And amid the criticism Cyrus has garnered for her headline-grabbing public appearances in recent months, Williams is quick to stand up for the one-time Disney star.
He tells Complex magazine, "I'm not worried about Miley. I've seen her soul in action. I know her voice, her voice is crazy. I keep saying it to everybody: You gotta remember, she's 21 years old and enjoying her life. She's enjoying her freedom."
"When you see her, when you read her words and you listen to her musical choices, and you look at what she's wearing - I'm not talking about when she goes on stage, I'm talking about her everyday dressing - she shuts it the f**k down.
"Now, when she goes on stage, she's expressing something else... She's expressing where she is in her life and her freedom. So while everybody else is being judgemental, they're not taking into account that she's been basically locked behind a camera all her life.
"And by the way, for good reason. All them years with Disney, and all them years with Billy Ray Cyrus as her dad and Dolly Parton as her godmother, did some good on that voice. But, you know, people are just watching her evolution of a young mind, but an old soul."