Fiona leaves Shameless in Season 9 because her character decides to move on from the South Side and start a new life for herself. Narratively, Fiona's story arc shows her growth from a caretaker for her family to an independent adult. She achieved financial security through an investment buyout, giving half of her $100,000 to her family while using the other half to start fresh elsewhere. This marks a turning point where she prioritizes her own well-being and aspirations after years of supporting her dysfunctional family.

On the actress side, Emmy Rossum, who played Fiona, left the show to pursue other projects and acting opportunities. Scheduling conflicts and a desire to expand her career beyond Shameless contributed to her exit. Rossum expressed gratitude for the role but felt it was time to move on after nine seasons.

Fiona's departure was crafted to be a meaningful and impactful sendoff, showing her growth and remaining ties to her family even as she chooses independence.