On 21 January 1919, Hogan and Dan Breen, together with Seán Treacy, Séamus Robinson and five other IRA members helped to ignite the conflict that was to become the Irish War of Independence. They shot dead two members of the Royal Irish Constabulary (RIC) - Constables McDonell and O’Connell - at Soloheadbeg in County Tipperary. The RIC men were transporting gelignite explosives, when they refused to surrender them, the IRA shot them dead. Robinson was the organiser of the action, while Treacy was the logistics expert.
"On the eventful day Dwyer saw the explosives, 160 pounds of gelignite, being loaded on a cart and heading off with a guard of two policemen. He cycled ahead and watched as they took the long route to the Soloheadbeg quarry. He took the short route and informed the anxious Volunteers of the convoy's size and movements. The horse was being led by two workmen, Edward Godfrey and Patrick Flynn, while the two policemen, Constables Patrick McDonnell and James O'Connell, walked behind with their rifles slung over their shoulders. As they passed Cranitch's Field near the quarry the policemen were called on to surrender by masked men. When they took up firing positions Seán Treacy, followed by Breen and Robinson, opened fire."
Treacy, Breen and Hogan took the cart and hid the explosives and immediately 'went on the run'. The met up again with Robinson a few weeks later and the "big four" as they were locally called, remained in hiding over the coming months, moving from house to house of sympathisers or sleeping in the rough in the countryside. Treacy and Robinson traveled to Dublin and met with Michael Collins who offered to arrange for them and Breen and Hogan to escape to America. They rejected the offer and told Collins they would remain in Ireland and continue the fight. 
After Hogan was arrested on 12 May 1919 three of the other men who were part of the Soloheadbeg ambush ( Dan Breen, Seán Treacy and Séamus Robinson) were joined by five men from IRA East Limerick Brigade in order to organise Hogan's rescue. Hogan was being transported by train to Cork on 13 May 1919, and the men, led by Treacy, boarded the train in Knocklong. A close-range shoot-out followed on the train. Treacy and Breen were seriously wounded in the gun fight, two policemen died, but Hogan was rescued. He was spirited away to Knocklong village where his handcuffs were cleaved by Séan Lynch, one of the rescuers, in the local butcher's shop.
After Knocklong the hunt for the big four intensified and they relocated to Dublin and undertook a range of missions under the direction of the Dublin leadership, some of these missions were in association with a unit known as The Squad . Plans were made and ambush positions taken for a number of attacks on Lord French British Viceroy and Commander of the British Army in Ireland, in the second half of 1919, however the intelligence received about French's movements was inaccurate and these ambushes didn't occur until the ambush at Ashtown road. In December 1919 Hogan, Treacy, Breen, Robinson, Martin Savage and a number of Dublin volunteers under the leadership of Paddy Daly undertook an ambush on Lord French's motorcade of three cars at Ashtown Road in Dublin. While 3 of French's party, 2 RIC and a driver, were wounded French got through unharmed, while Martin Savage was killed and Breen wounded.
Hogan returned to Tipperary in the middle of 1920 serving as a battalion officer in the Third Tipperary Brigade before being made O/C of the Brigade's 2nd Flying column in December of 1920.
Hogan took no part in the Civil War. He went back to farming in Donohill but sold the farm some time afterwards, he then bought a vegetable farm in County Dublin but this venture did not succeed. He married Christina Butler and had three sons; Hugh, Thomas and Sean. In later years he was in poor circumstances, he lived on his own in North Great George's Street, Dublin. Due to illness in his later years his memory was not quite so clear and his handwriting was almost illegible. He was also very disillusioned with the way the Irish people had developed their country from the time the Republic of Ireland gained freedom. Hogan stayed with Seamus Robinson and his family in their house on Highfield Road close to his death. He died aged sixty-seven on Christmas Eve 1968. His death was reported RTÉ. He is buried in the family grave in Tipperary town.
- Irish Bureau of military History- Seamus Robinson's witness statement - Statement 1721
- Ryan, Desmond (1945). Sean Treacy and the Third Tipperary Brigade I.R.A. Kerryman Limited.
- My Fight For Irish Freedom, Dan Breen, 1989. PB) ISBN 0-947962-33-6
- Irish Bureau of military History- Maurice McGrath's witness statement - Statement 1701
- Brendan A. Creaner. "The Rescue at Knocklong". Knocklong-Rescue.com. Retrieved 8 December 2006.
- Jim Maher (1988). The Flying Column - West Kilkenny 1916-1921. Geography Publications.