Sienna Miller and Margot Robbie Showed Me the Cool-Girl Way to Wear Denim Right Now

If I trust any two people to take my spring/summer styling inspiration from, it has to be Margot Robbie and Sienna Miller. Having both spent years working with big-name brands and in-demand stylists, the two have cultivated chic and distinct wardrobes that emanate elegance and an undone ease.
So when they both back the same trend, within a day of each other, no less—you know it’s worth paying attention to. Stepping out in London this week, the two put their force behind the oversized double denim co-ord trend—and I'm inspired.
Leaning into the relaxed nature of the casual denim trend, Robbie styled her set without excessive accessories, selecting a simple black shoulder bag to add a point of polish without overcomplicating her styling.
Meanwhile, Miller attended an event in London, layering a long-line denim shacket in a boxy, oversized fit over a pair of wide-leg jeans, complete with a sheer, printed blouse. Using accessories to enhance her styling, Miller selected a supple suede bag, a square buckle belt and brown Gucci Suede Horsebit Ballet Flats (£695) to complete her day-time look.
After making waves on the spring/summer 2025 runways in September, oversized double denim has solidified its place as a fashion frontrunner for the warmer months. Chanel, Stella McCartney, and Gabriela Hearst were among the brands championing the trend, styling their denim pieces in a notably undone manner that expressed a move towards nonchalant cool.
Model wears baggy double denim on the Stella McCartney spring/summer 2025 runway.
Beyond the runways and celebrity circles, the trend has already gained traction among Instagram’s most stylish. Styling their sets with pointed-toe heels to add some structure and height or going all-in on comfort and trying out co-ords with rounded-toe flats for a simple flat-shoe option, this oversized look is proving its versatility this season.
Unlike slim-fitting denim sets, which can feel restrictive as temperatures rise, the loose, breathable nature of oversized double denim offers both style and comfort while also taking note of the jumbo wide-leg jeans trend that continues to thrive.
While denim-on-denim has had its fair share of highs and lows in the fashion cycle, this ultra-relaxed version is primed for a major moment. Ready to embrace the trend? Scroll on for my edit of the best denim two-pieces to shop now.
SHOP OVERSIZED DOUBLE DENIM CO-ORDS:
Style this over a white tee for an easy, day-to-day look.
Marks & Spencer's barrel leg jeans are a favourite within fashion circles.
I always come back to Citizens of Humanity for their chic denim collection.
The pleated jeans trend is set to take off this spring.
The bomber jacket silhouette ensures a roomy, comfortable fit.
Style with chunky trainers or wear with a neat ballet flat.
Natalie Munro is Who What Wear UK’s news writer and has worked in the fashion industry since she graduated with a degree in Journalism from the University of the Arts London. Natalie’s experience in the industry spans journalistic and styling roles that have seen her work for publications including British Vogue, Conde Nast Traveller, Vogue Ukraine, AnOther Magazine and Elle UK.
With an interest in uncovering the latest fashion trends, Natalie takes a leading role in identifying news for Who What Wear UK. Reporting on a daily basis, Natalie focuses on trends on and off the runway, as well as street style and celebrity fashion. Natalie also creates content for Who What Wear’s social channels including TikTok and Instagram on a weekly basis.
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