Appointed Director in 1923, Lucius O’Callaghan (1877-1954) had the task of preparing the Gallery for reopening. In mid-1922 the Gallery had closed its doors to the public due to the ongoing unrest in Dublin that accompanied the Irish Civil War. In February 1924, a letter from the Ministry of Home Affairs stated that ‘there were no longer any military considerations to interfere with the opening of the Gallery… , and … the Director should take immediate steps to bring the Gallery staff to full strength and to arrange with the Minister for a full or partial opening of the Gallery’.
O'Callaghan was a connoisseur and collector of paintings, particularly seventeenth century Dutch works, and of antique furniture and porcelain. He was a member of the RHA, an ex-President of the Royal Institute of Architects of Ireland and in 1917 was appointed as a member of the Board of the Gallery. Board members Thomas Bodkin and Hutchenson Poe, criticised O’Callaghan's appointment as Director, believing that he was not qualified for the position. Between 1923 and 1927, however, he managed the Gallery proficiently, dealing with the changes brought about by the Irish Free State and the Department of Education, which assumed responsibility for the Gallery’s affairs.
Collection developments during the 1920s included the Edward Martyn (1859-1923) bequest of seven paintings including works by Corot, Monet and Degas. In 1925 the Gallery received its first gift through the Friends of the National Collections of Ireland- a drawing entitled, Silenus and King Midas by Giuseppe Passeri. O’Callaghan also purchased Pieter Lastman’s Joseph selling the corn and A Sick Call by Irish artist, Matthew James Lawless.
Throughout his tenure as Director, O'Callaghan had continued to practise as an architect, and in June 1927 he resigned to focus on architecture.