Walsh-Peelo attended Coláiste Ráithín, a Gaelscoil (an Irish language-medium school) in Bray, and Wicklow Educate Together National School in County Wicklow. He began his musical career at age seven singing soprano and being coached by his mother, soprano Toni Walsh. He won many prizes and was eventually cast in Mozart's Magic Flute when he was twelve, which toured Ireland.
He made his acting debut in the film Sing Street. He sings and plays guitar and piano with his Sing Street co-star Mark McKenna. He was signed by William Morris Endeavor in the United States and Independent Talent in the United Kingdom in 2015. He is also the Ambassador for UNICEF Ireland's program "Emergency Lessons," aimed at providing education to children caught up in emergencies.
- Walsh-Peelo appeared on Busker TV's YouTube channel with his then band, Guru, performing a cover of Paul Nutini's "Pencil Full Of Lead."
- When he was fourteen in 2013, Walsh-Peelo cut his twelve-inch long hair to contribute to the Rapunzel Foundation, which collects hair to make Freedom Wigs and also raises funds to help people buy Freedom Wigs.