Tisagenlecleucel offers promise to children with relapsed/refractory (r/r) acute lymphoblastic leukemia (ALL). However, there is limited experience with and data supporting the use of tisagenlecleucel in infants. We describe our successful experience using tisagenlecleucel followed by a haploidentical donor hematopoietic stem cell transplantation in an infant with r/r KMT2A-rearranged ALL, the youngest infant to survive and achieve prolonged remission using this approach.