Blanchard was born in Los Angeles, California, to Elizabeth and Mark Blanchard-Boulbol, who are yoga instructors. Her paternal grandfather was an immigrant from the Middle East, who had paternal Syrian ancestry and maternal Armenian ancestry, and her paternal grandmother's ancestors are from England, Denmark, and Sweden. Her paternal great grandparents had met in Aleppo, present-day Syria. She was named after a character in Anne Rice's The Witching Hour. Rowan has two younger siblings, Carmen and Shane.