Assoulin grew up in Brooklyn and had her first taste of the fashion industry at 14, when she began a four-year internship at Lee Angel, the jewellery brand designed by her future mother-in-law, Roxanne Assoulin. Assoulin enrolled at New York’s Fashion Institute of Technology , but dropped out to intern at Oscar de la Renta , followed by work placements at Adam Lippes, Bryan Reyes and Lanvin's design studio in Paris.
Her eponymous label launched its debut collection for Resort 2014 and, the following year, Assoulin received the CFDA’s emerging womenswear designer of the year award. Also in 2015, the brand launched a jewellery collaboration with Swarovski and won Swarovski's Collective Award in 2016. The brand’s high-profile admirers include Karlie Kloss and Beyoncé, who wore one of Assoulin’s designs in her visual album, Lemonade. Today, she is known for her elegant and whimsical daywear and counts Moda Operandi and Net-a-Porter among the brand's stockists.