Joe Dennigan was born in Ballycormack, County Longford in 1910. In his early career as a journalist, he worked for the regional press, namely The Longford Leader from 1925–8, and The Offaly Chronicle from 1929–30. On the formation of The Irish Press, he moved to Dublin to become its political correspondent. The newspaper asked him to accompany the Free State delegation to the Imperial Conference in Ottawa, Canada in 1932 and he became a well known and respected journalist and made many contacts abroad.

In 1933, the Government outlawed General Eoin O'Duffy's Young Ireland Association, formerly known as the National Guard and commonly referred to as the Blueshirts. Dennigan wrote an article for The Irish Press on the announcement of the proclamation and stated that a government source had informed him that a few days grace to leave the Association would be given to its members. However, Commandant E.J. Cronin, the secretary of the Young Ireland Association, was arrested before the notice banning the organisation had been posted in Iris Oifigiúil. He was charged with sedition and membership of an unlawful association and brought before a Military Tribunal in Collins Barracks. Counsel for Cronin called Dennigan as a witness to the defence and asked him to disclose the source who had informed him of the reported amnesty, an amnesty which Cronin claimed was not extended to him.

Dennigan steadfastly refused to reveal the information citing professional ethics as his main reason. As a result he was sentenced to a month's imprisonment in Arbour Hill Detention Barracks and became the first journalist in Irish history to be imprisoned for not disclosing his sources. The case caused a national and international outcry, especially amongst journalists, and Dennigan was treated like a hero on his release in January 1934.

Dennigan continued working for The Irish Press for a number of years. In 1950 his health failed and he died suddenly on 15 June.