Mahr became a highly controversial figure in twentieth-century Irish history owing to his early leadership of the Dublin Nazi chapter, and propaganda broadcasting from Germany,[1]: 17  and was not allowed to return to his role after the Second World War.

One of his key achievements was the production of a card index of excavations and finds, and he also drove a return to active archaeological dig work, after an interval of decades.

In 1934 Éamon de Valera appointed Mahr as the director of the museum, for which he built an international reputation through creativity and dedication.

De Valera was so impressed with his commitment that he wrote him a personal cheque for one excavation project, in Drimnagh, Dublin, for what was then a considerable sum.

Notwithstanding his leadership of the local Nazi organisation, Mahr worked with wealthy Jewish donor, Albert Bender of San Francisco, and they exchanged letters over several years.

Mahr was arrested and accused of being a Nazi spy, with a claim that he used his position as Director of the National Museum to plan Hitler's invasion of Ireland.

[1] Mahr sought to return to his directorship, and the Taoiseach was originally in favour, given his achievements, but there was opposition from Ireland's Head of Military Intelligence, and a vocal TD, James Dillon.

[...] Into this appalling scene, stepping over dead people and horses, and the rubble of Berlin's once-magnificent buildings, came Hilde Mahr, an eighteen-year-old from Dublin.