David Patrick Moran, the son of a builder, was born in Waterford in 1871. He was educated in Mount Sion schools and later in St. Vincent’s College, Castleknock. On leaving school he went to London where he gained his first journalistic appointment at the Star newspaper, founded by T.P.O’Connor. Moran was attracted to the Irish language movement and, through it, to Irish nationalism, during his thirteen years in London. In 1898 he returned to Dublin and joined the Gaelic League. He married Teresa O'Toole, the daughter of Captain O'Toole, an intimate of Parnell and Mayor of Waterford on three occasions in the 1890's. Moran was brother of Mr. E. P. Moran, a prominent lawyer in the U.S.A. and Ireland who was specially briefed with a number of American colleagues to defend O'Donnell, after O'Donnell was charged with the murder of Carey, the informer of the Phoenix Park assassins.

In 1900 he founded the Leader, an outspoken weekly publication that played a very important part in the development of the cultural and national aspects of the Irish character. The Leader was an immediate success. A special horse and cart was engaged to supply newsagents, so great was the demand. He was a gifted and vigorous writer with a keen intellect that was tinged with a deep sarcasm. He had a gift for name-calling and abuse and he used his paper to excoriate and decry the faults and failings of other nationalists. 

The Leader attracted a lot of Irish advertising and Moran saw the publicising of Irish goods as one of its main roles. He advocated "buy Irish" campaigns but sensibly warned that the Irish people would buy Irish goods only if they were "as good and as cheap" as imports.

Moran supported the industrial development authorities set up in some Irish towns from 1903 onwards. Small and middle-sized businesses were represented in these, unlike the bigger and older enterprises that dominated the chambers of commerce. Moran attacked the latter as "chambers of importers", run by Protestants and a few "west-British" Catholics such as William Martin Murphy. The Leader took regular swipes at Murphy, and especially at his "ha'penny dreadful", the Irish Independent. He ridiculed the English culture of cheap papers and music-hall entertainment, associating The Irish Times with this subculture by dubbing it "Alf Fox" (the pen-name of the paper's horse-race tipster) or, less subtly, "The Bigot's Dustbin". He knew Ireland must provide its own cheap popular culture and he thought that this could be done by the Gaelic League with its concerts and ceilithe.

Moran put forward his view of Irishness in The Leader and in his 1905 book The Philosophy of Irish Ireland. In Moran's view Ireland and England were at war in what he called 'the battle of two civilisations.' For Moran the two civilisations consisted of Catholic nationalists and Protestant unionists. The nationalist weapons in this war were the Irish language and the Catholic religion. He believed that the vast majority of Protestants could not be truly Irish though he was ready to admit that there were some individual Protestants who contributed to the welfare of the country.

He was a 'Mitchelite' in that he believed that Ireland's only crime was 'her proximity to Britain.' He rejected all links between Ireland and Britain. He portrayed Irish Protestants as an alien garrison that dominated the the true Irish people through their control of the political, judicial and economic levers of power, exercised through secret organisations such as the Freemasons. He did not, however, call for the expulsion of these Protestants but hoped, one day, that they would be assimilated into the mainstream Catholic population. Moran's weapon was mockery and the invention of crude, but funny, appellations for those he criticised. 

Moran lived on the edge of the then independent township of Rathmines, which had a large Protestant middle-class population. On his way home on a tram, shortly after Queen Victoria's death, he gazed at the long faces of many of the commuters, ostentatiously mourning the dead monarch, and coined his most famous nickname: "Sourface". He repeatedly denied it was a synonym for Protestant, claiming instead that it connoted an affectation of superiority. He reserved his most bitter invective for those middle-class Catholics - 'West Britons' and 'Castle Catholics' he called them -  who, to his mind had 'sold-out' their heritage. These were the rising, pushy group of Catholics who made their money through trade or in the professions and who were now adopting the sports, accents and even the politics of the Protestant class who ruled the country.  

He condemned the Irish Parliamentary Party which, he said, was corrupted and seduced by it's activities in the Westminster parliament. He admired Redmond and Tim Healy as writers and statesmen but he disliked John Dillon and William O'Brien. In his novel, Tom O'Reilly, he portrayed O'Brien as 'John Francis Xavier High Faluter O'Brien.' He despised those nationalist politicians who flattered their uneducated listeners into supporting them by their sentimental speeches full of 'ráiméis' and he was very condemnatory of the link between the Home Rule leaders and publicans - 'Mr. Bung' - because he believed that alcoholic drink undermined the health of the nation and was the cause of so many of Irelands social ills. He had the support of a number of Catholic movements that energed about that time. These included the 'Temperance Crusade' which campaigned against excessive drinking and the 'Literature Crusade' which attacked British newspapers on the grounds that they were corrupting Irish morals.

Moran was equally as hard on Arthur Griffith's Sinn Féin and he described its members as 'tin-pikers.' When Griffith put forward his dual-monarchy proposal based on the Austro-Hungarian model, Moran called them "The Green Hungarian Band".

He attacked the co-operative movement because some if its leaders were Protestant and he disliked, intensely, the Irish Literary Revival and its leaders. He believed that Irish literature in English was a contradiction and an absurdity and that the Irish language was the only logical medium for Irish literature. He felt that Yeats was a second-rate poet and a 'crypto-Protestant con-man' and he called George Russell (AE) the 'Hairy-Fairy' (referring to his huge beard and his interest in the occult)and described him as a 'half-baked Orangeman.' 

He welcomed the new Dáil and was delighted that the first meeting was conducted entirely in Irish. After the Treaty, which he supported, he urged both sides to settle down as government and opposition. He was appalled at the Civil War: he believed that since the Irish people had voted for the Treaty it should have been accepted by the politicians. 

Moran died suddenly on January 31,1936. He was survived by two sons and one daughter, Nuala, who took over as editor of The Leader. She changed the paper's emphasis and under her editorship the paper covered more social and cultural items. The paper ceased publication in 1971.

    The historian, Patrick Maume has argued that Moran was a bigot, but because of his sense of humour, self-awareness and interest in the exchange of ideas, he never sank to the level of the "hate-filled diatribes" produced by J.J. O'Kelly in the Catholic Bulletin. Brian Maye wrote of him in the Irish Times, "Moran was a brilliant journalist, a talented businessman and an important spokesman for the rising Catholic entrepreneurial class. He greatly influenced his own generation and the Leader provided an important forum for debate in the crucial period between the fall of Parnell and the Easter Rising."