Daniel Breen (10 October 1894 – 27 December 1969) was an Irish republican. He was member of the Irish Republican Army during the Irish War of Independence and the Irish Civil War and was wounded a number of times. In later years he was a Fianna Fáil politician.

Breen was born 10 October 1894 in Grange, Donohill parish, County Tipperary, to Daniel Breen Senior and Honora Moore. He was the second-youngest of eight siblings. His father died in May 1901 when Breen was six, leaving the family very poor. He was educated locally, before becoming a plasterer and later a linesman on the Great Southern Railways.

Breen was sworn into the Irish Republican Brotherhood in 1912 and the Irish Volunteers in 1914. On 21 January 1919, the day the First Dáil met in Dublin, Breen – who described himself as "a soldier first and foremost" – took part in the Soloheadbeg ambush. The ambush party of eight men, led by Séumas Robinson, attacked two Royal Irish Constabulary men who were escorting explosives to a quarry. The two policemen, James McDonnell and Patrick O'Connell, were fatally shot during the incident. The ambush is considered to be the first incident of the Irish War of Independence and was carried out with the help of intelligence supplied by Breen's younger brother and fellow Volunteer Laurence (1900–1940); "Lar" Breen, then aged 18, was imprisoned for "seditious" activities.

Breen later recalled:

"… we took the action deliberately, having thought over the matter and talked it over between us. [Seán] Treacy had stated to me that the only way of starting a war was to kill someone, and we wanted to start a war, so we intended to kill some of the police whom we looked upon as the foremost and most important branch of the enemy forces ... The only regret that we had following the ambush was that there were only two policemen in it, instead of the six we had expected …"

However, Robinson, wrote:

"It was laid down as an order that if only two RIC should accompany the cart they were to be challenged, but if there were six of them they were to be met with a volley as the cart reached the gate. The reason for the difference was that there would be so little danger to us if only two appeared that it would be inhuman not to give them an opportunity of surrendering, but if six police turned up they, with their rifles, would be too great a danger to the eight of us to take any such risk as to challenge them and thus hand over our initiative. We had only one Winchester Repeater rifle and an agglomeration of small-arms."

In the same statement, Robinson described the two policemen as he and Paddy Dwyer jumped out and seized the reins of the horse: "The RIC seemed to be at first amused at the sight of Dan Breen's burly figure with nose and mouth covered with a handkerchief; but with a sweeping glance they saw his revolver and Dwyer and me they could see only three of us. In a flash their rifles were brought up, the bolts worked and triggers pressed two shots rang out, but not from the carbines: the cut-off had been overlooked: The two shots came from Treacy and Tim Crowe. Those shots were the signal for general firing. At the inquest the fatal wounds were 'caused by small-calibre bullets'."