Beatrice Borromeo Casiraghi was born in San Candido, Italy on August 18, 1985. Her parents are Don Carlo Ferdinando Borromeo and Countess Donna Paola Marzotto. Beatrice was born into the House of Borromeo, an aristocratic family that comes from old Milanese wealth. Descendants from this house include counts, cardinals, and even an archbishop. Her mother, Paola, also comes from old money, as her family is one of the key players in the Italian textile business.

Despite having two children together, Beatrice's parents never got married. She has a total of four siblings, including her biological older brother, Carlo Ferdinando Borromeo, and three step-siblings from her father's previous marriage to model Marion Sibylle Gabriele Zot: Isabella Borromeo, Lavinia Borromeo, and Matilde Borromeo.

As a child, Beatrice was aware that she lived a more privileged life than others. Though she was in denial at the time, she eventually came to terms with it. "When I was little, I would have wanted to be like any other girl, but the reality is that I was not," she shared with Vanity Fair Spain. Despite growing up comfortably, Beatrice still respects the value of money, which she attributes to her mother. "In my house, money has always had the right weight. My mom taught me to respect them," Beatrice explained to Corriere della Sera.