Margot Robbie 's fantabulously emancipating her famous posterior ... wearing a dress so sheer her entire backside was on display while she walked the red carpet!

The actress hit the "A Big Bold Beautiful Journey" premiere in the United Kingdom Thursday ... and, when she turned around, we got an eyeful of her 'Bombshell' bottom.

Ya gotta see the pics for yourself ... Margot's glittering from chest to toes in a sparkling dress -- with jewels obscuring the otherwise completely sheer fabric. Getty

We can't see everything Margot's workin' with ... but, we can see a whole lot -- including a hint of the thong that's doing nothing to cover her up.

She's also sporting a whole lotta sideboob ... clearly not wearing a bra in this outfit -- and, we're sure it got one or two overexcited peop

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