During his early years, he became heavily involved in politics after he qualified as a solicitor and set up a practice at 66 Dame Street in Dublin.

As a keen supporter of Irish independence, Duggan fought in the 1916 Easter Rising; however, following its failure he was subject to court-martial and was sentenced to three years penal servitude.

[7] In 1916, Duggan was part of Commandant Daly and therefore was serving in the North Dublin Union in the days approaching the 1916 Rising and afterwards Father Matthew Hall.

Duggan's efforts to get medical assistance were unsuccessful at Richmond Hospital as the British officer who responded to the call declined the message and didn't allow it to go through.

In Duggan's region, the volunteers suffered very few injuries with the most violent fighting taking place on Friday night and Saturday morning.

Duggan engaged in the War of Independence and his role in this was the IRA's Director of Intelligence, this came to an end in November 1920 when he was imprisoned again and was not released until the Anglo-Irish Truce of July 1921.

[10] When the truce concluded, Duggan was authorised as one out of the five envoys to discuss and finalise the treaty with the British Prime Minister David Lloyd George.

Duggan also wrote about his participation in Sinn Féin how he was released in 1917, and 1918, how he was triumphant in being a candidate for the South Meath constituency.

In one of his letters, which Duggan wrote on 25 April 1916, he referenced 'the whole damn family' consisting of information as to how his volunteers and he were being 'treated as princes' by the nuns in the convent nearby, receiving help from the children in the area and building barricades.

In his letter, Duggan also writes about morale amongst his comrades and hearing rumours about a German who had landed in County Kerry.