The concept of relationship completion is embodied as the core belief for end-of-life care in Taiwan, known as the Four Expressions in Life. No studies have been published investigating and trying to understand how music therapy facilitates the Four Expressions in Life. This convergent mixed-methods study examined the effects of music therapy to facilitate relationship completion for patients at the end of life and their families in Taiwan, and explored their personal experiences in music therapy sessions. Thirty-four patients at end-of-life care and 36 of their family members participated in a single music therapy session with a one-group pretest-posttest design using standardized quality-of-life measures for patients at the end of life and families. A nested sample of 5 patients and 9 family members completed semi-structured interviews. Significant differences between the pre and post session scores were revealed for patients in the Life Completion subscale of the QUAL-E (p < .001), and the global QoL Indicator (p < .001), and for families in the Completion subscale of the QUAL-E (Fam) (p < .001), and the Overall Quality of Life (p < .001). Four themes around opportunities emerged from the interviews: the opportunity for exploration, for connection, for expression, and for healing. The integrated findings suggest that music therapy facilitated relationship completion and improved quality of life for both patients and their families. Furthermore, this study supports that the transformative level of music therapy practice within a single session for end-of-life care is attainable.