[1] The hospital was founded by Dr Kathleen Lynn and Madeleine ffrench-Mullen with the help of Sinn Féin activists in 1919 and was housed in an old Georgian house constructed around the year 1770.

The building was in a state of disrepair and was reputed to have once been a shooting hall used by Lord Charlemont.

Earlier in her career, Lynn had experienced discrimination in applying for hospital positions due to her gender, and Saint Ultan's was the only hospital in Ireland entirely managed by women.

[6] Dr Barbara Stokes, specialist in children with disabilities, also worked at the hospital.

[9][10] The site became part of the Charlemont Clinic, a private medical clinic which operated until 2014, when it was sold to the Dalata Hotel Group for redevelopment as the Clayton Hotel Charlemont, which opened in 2018.