This week, the stunning British actress was spotted strolling through the streets of Manhattan with the perfect companion - her adorable four-year-old daughter.
In fact, it appears the only thing that can out-chic the Big Apple was the pretty blonde and her doppelganger daughter.
These ladies know how to make a statement.
Sienna, 34, braved the cool fall weather with a thick wool coat, knitted pastel beanie, completed with cute shades.
While Marlowe was a spot of sunshine, donning a bright canary yellow coat, pleated baby pink tights with the loveliest pom pom beanie.
Sienna, who shares Marlowe with her former longtime love Tom Sturridge, spoke candidly about the truth behind being a mother.
Sitting down for the October 2015 issue of Vogue UK, the 34-year-old admitted that life had been "really quite overwhelming recently, just with the volume of everything going on."
"Everything's shifting," she explained.
"It's actually been the s--ttiest year, and amazing. It's always yin and yang. I feel like if you're excelling in one area, it's hard to manage both and I do feel like the work is going really well."
At the time, Sienna had just come out of two years packed with filming, including Foxcatcher and American Sniper.
This was all the while dealing with the break-up of her partner of four years and Marlowe's dad, Tom Sturridge. The pair called time on their relationship last July.
"Obviously when you have a baby it's the most incredible experience but your life is also catapulted into this chaos and you are exhausted," Sienna divulged to the fashion title.
"I could literally get on this table and fall asleep."
Admitting, "I'd like to be better at managing things; I'd like to be more super — although we're never going to feel it, even if we are."
"That's the curse of motherhood — we just run ourselves ragged."
"I'm just trying to get a sense of what that guilt is. I sometimes feel like it's a totally invented emotion. It's strange to be punishing ourselves this way. It's not healthy."
Despite the hard work, Sienna wouldn't change a thing, having once mused that welcoming her daughter "was like, 'There you are — that's what I have been missing.' Like we're both in on something only we know. An amazing sense of being complicit with a little being."
And it would appear the chaos of life with a toddler has settled.
With Marlowe now four, Sienna has been able to focus on her love life.
The actress is rumoured to be dating her Foxcatcher director Bennett Miller.
The couple, who've stepped out on numerous occasions, opted for a more public date, attending the US Open earlier this year.
The pair were first linked together back in May after an eyewitness told Us Weekly, "[Sienna and Bennett] were together all night [at a Met Gala after party]."