She's been channeling her character Emily Nelson in the new film A Simple Favor, and like Lively, Nelson is constantly wearing the menswear-inspired ensemble in the movie, in which Stephanie Smothers, played by Anna Kendrick, is trying to uncover the mystery behind her friend's sudden disappearance.
While Kendrick's outfits are girly and youthful (in line with her mommy vlogger character), Lively's borrowed-from-the-boys, tailored costumes are dapper as she commits to fashion-forward power dressing, which involves lots of Ralph Lauren suits and Christian Louboutin shoes.
Take a peek at the actresses' getups ahead, and see them on the big screen come Sept. 14.
Lively wears a three-piece Ralph Lauren pinstriped suit adorned with pocket watch, detachable cuffs and custom hat from The Saucy Milliner. Kendrick wears a yellow Brooks Brothers raincoat and Hunter boots.
Lively in a black Ralph Lauren jacket, pants and cummerbund with J.Crew bow tie. Kendrick in a Kate Spade New York dress and Pilcro denim jacket.
Lively rocked a similar look for Ralph Lauren's 50th anniversary show during New York Fashion Week. At the film's New York City premiere on Monday, she dished to ET that she loved the designer's suits during filming so much that she requested them again to secretly keep for herself.
"I called in some of the looks from the Ralph Lauren suits for the Ralph Lauren event and they were like, 'You wore these in the movie, why would you wanna, you know, call in these suits again? You're not gonna wear them for the press tour.' And I was like, 'Yeah I know, I'm keeping them now. I forgot to keep them then, so I'm acting like I'm wearing them for the press tour and that I may wear them and then stocking them in my closet.'"
Lively in a cream striped double-breasted two-piece Ralph Lauren suit with cane, undone bow tie with pins and pocket watch.
The blonde took a break from suiting up to sport a gorgeous floral A-line dress by Samantha Sung and sparkly Christian Louboutin pumps.