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.
She did a great job in her roles.
For me it was Steven Van Zandt as Silvio Dante in The Sopranos. His bottom lip is one of the best visual running gags in the series.
R. Lee Ermey / Full Metal Jacket?
For those not in the know, Ermey was only ever meant to be a consultant to teach Tim Colceri, the actor playing the drill instructor, how to do so realistically. It was only after Ermey did a 30 minute demonstration in which he berated and insulted the “troops” of the film while stagehands beaned him with tennis balls and oranges that Kubrick realized that casting Ermey would essentially just be removing the middleman.
Andy Buckley, the guy who played David Wallace on The Office. He was a financial advisor at the time and they wanted him because he looked/sounded like an executive. Totally knocked it out of the park.
Tom Waits in The Ballad of Buster Scruggs. Sure it wasn’t his first time acting but I’d argue he’s much more well known as a musical artist and his performance was great.
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.
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.
I thought Anthony Edwards did a great job playing the antagonist in Hustle.
Haven’t seen it yet but heard Kevin Garnett killed it in Uncut Gems.
Justin Timberlake usually do a really good job, as a lead i.e. In Time, or in a supporting role like in Social Network.
At first I was like, what is Anthony Edwards famous for if not for his roles as Goose, or Dr. Green?
Revenge of the Nerds?