Bernstein graduated from William A. Shine Great Neck South High School in 2010. Bernstein attended the University of Wisconsin-Madison where she studied retail and then transferred to the Fashion Institute of Technology in New York City. She left school to devote more time to her blog and turn it into a career.

In 2011, Bernstein started WeWoreWhat as a street style photographer, which soon after transitioned into a personal style blog, as her Instagram account @WeWoreWhat gained popularity. In 2016, Bernstein launched a line of overalls called Second Skin Overalls, a direct to consumer brand. In 2017 at the age of 24, Danielle was placed on the Forbes 30 Under 30 list. In 2017 Bernstein designed a swimwear collaboration with Onia that exclusively sold at Intermix and was their best selling suit that Summer. The collaboration followed with two others, which the second of the two, an Italy inspired collection, drove over $3 million in sales total. Because of the success of their collaboration, in 2019 she launched her own swimwear line with Onia as her partners. In 2019, Bernstein teamed up with premium denim brand Joe’s Jeans to design and release a new style of jeans, called the Danielle Jean. She is the first blogger and influencer to have a product collaboration with the company, and it led to a second collaboration with them that had added styles. In 2020, she made the decision to bring all her brands under one roof with the launch of Shop WeWoreWhat which included swim, denim, overalls, and most recently added active.

In multiple instances, Bernstein has been noted for copying others’ designs. In 2018, Bernstein received attention for copying the designs of various jewelry brands when she launched a series of products with Nordstrom. Foundrae, a specialized jewelry line, said that she had created nearly identical pieces after an earlier visit to the company’s studio. Bernstein subsequently apologized in a tear-filled Instagram post and withdrew the copied pieces from the collection. In 2020, Bernstein announced a design for a cloth face mask with a chain. Fashion watchdog group Diet Prada, an Instagram account dedicated to highlighting instances of design copying, observed the mask was nearly identical to a patent-pending model created by a Latinx brand called Second Wind. Bernstein had earlier requested free samples from the company. Bernstein denied that she had copied the design from Second Wind. Days later, Bernstein posted to Instagram a photo of herself wearing what she claimed were a vintage pair of gym shorts, writing in the caption that she would be remaking the shorts to sell. The shorts were actually from an Etsy shop run by an Australian brand, Art Garments. After the Etsy seller published a receipt showing Bernstein had purchased the shorts from their store, Bernstein edited the Instagram caption to read, “CORRECTION – these are from Etsy and I totally thought they were vintage but they are made to order – someone on my team ordered them for me a while back – I will not be making them!” In August 2020, a Brooklyn lingerie store alleged that Bernstein had copied their signature design, which they use on tissue packaging, and used it on swimwear and as print wallpaper.

In March of 2020, Bernstein launched a namesake brand exclusively at Macy’s called, Danielle Bernstein. The debut Spring collection was all priced under $100 and had a size range of 00-24, becoming Bernstein’s first size-inclusive line. Along with the launch, Bernstein had a campaign shoot modeled by real-life followers, featuring women with different body shapes and types so that anyone could see themselves wearing the line. The first collection sold $1 million in the first 2 hours, and $2 million after 24 hours. The Danielle Bernstein Summer line launched in June 2020, and featured vintage inspired dresses and cute sets.

In May 2020, Bernstein published an autobiography, This is Not a Fashion Story: Taking Chances, Breaking Rules, and Being a Boss in the Big City. She wrote about her personal life and her entrepreneurial journey.The book appeared on the New York Times Best Sellers list and was featured on the ‘Business List.’ However, the New York Times has since placed a “dagger” symbol alongside the book, indicating its listing includes suspicious “bulk purchases.”

In September 2020, Bernstein was diagnosed with the coronavirus. She previously had been socializing in the Hamptons without a mask, prompting criticism for failing to follow CDC guidelines.

In January 2020, a clothing reseller posted swimwear for sale on the Poshmark platform, not realizing it was unreleased samples of Bernstein’s swimwear collaboration with Onia. The samples had been accidentally donated to Goodwill by a showroom employee, where the reseller purchased them to sell online. Bernstein and the seller came to an agreement in which the reseller would remove the pieces from her store and sell them back to Bernstein. However, they argued over whether Bernstein had agreed to reimburse the costs of the swimwear as paid to Goodwill, or the seller’s listed resale prices. Fearing the release of her new line, Bernstein spoke to the Poshmark CEO to halt the sale of the swimwear was put back up for sale. A Change.org petition was created titled “Pledge to Boycott Poshmark if they Continue to Allow the Bullying of Small Business.” Eventually, Bernstein and the reseller met in person and came to an agreement where the reseller was given merchandise from the previously collection to sell at a greater value.