Tricia Helfer comes to mind first. In Battlestar galactica. I forget the story but it’s something like she was brought in for her looks(they wanted a knockout for the first scene cylon). Then she went on to blow them away with her acting. She was a model before if I recall.

Eminem in 8 Mile. When I first saw it I was convinced he’d become a superstar actor and stop making music, but that never happened. Even so, he’s fucking phenomenal in that movie.

R. Lee Ermey / Full Metal Jacket?

Dominique Tipper in The Expanse (E: yeah, not a movie, but still an awesome experience all around)

I mean, not everyone in the community thinks much of her acting, but on Season 5 she puts out a performance that puts a lot of veteran actors to shame.

Here’s another more niche example:

Frank Silva as “Bob” on Twin Peaks. He was a set dresser who worked with David Lynch and Lynch liked his look so much they made the character for him. Now he’s regarded as one of the better tv villains.