The IRA in West Mayo was relatively quiet until January 1921, when Michael Kilroy, who was described as, "a puritanical and ascetic blacksmith"[2] took over command of the brigade after the previous leader Thomas Derrig was arrested by the British.

On 22 March 1921 Kilroy and two comrades, Joe Ring and Brodie Malone Armed with a Mauser revolver chanced upon a sergeant and three constables of an Royal Irish Constabulary (RIC) patrol beside Westport road near Carrowkennedy.

On 23 May 1921, they were forced to retreat when a patrol from Newport came into the village, but the men of the West Mayo Brigade held them off and the wounded were got away to safety.

The column was hidden in the hills of the Nephin range and in the Glenisland area until the RIC, Tans and the Border Regiment lifted the cordon.

One volunteer, Jim Browne from Drumgarve, Kilmeena, was killed at Skirdagh and a number of the RIC, including a district inspector, died.

The Crown forces burned houses, including the home of Michael Kilroy, on 20 May 1921 and the same would happen after the Carrowkennedy Ambush in June 1921.

On 2 June 1921, in an action at Carrowkennedy, eight Tans were killed and 16 members of the RIC, along with a Lewis Machine gun, rifles and ammunition, were taken.

[2] Kilroy opposed the Anglo-Irish Treaty in 1922 and sided with the Anti-Treaty IRA during the Civil War with the Irish Free State forces in 1922–23.

In the early months of the Civil War, he and his men dominated the West Mayo area and successfully ambushed Free State Army troops on several occasions.

However, the Free State then sent an expedition to the North Mayo/Connemara area, which succeeded, after some fighting, in capturing Kilroy and many of his men at Carrowbeg House on 23 November 1922.

Kilroy was the leader of the Mounjoy internees during the 1923 Irish Hunger Strikes and made the position of the prisoners clear: "Each of us, to himself and his comrades, solemnly pledges to refrain from food until he is unconditionally released.

Our lives and the suffering we shall endure we offer to God for the furtherance of the cause of truth and justice in every land and for the speeding of the day of Irelands freedom.

The Fianna Fáil Cumann in Newport is named in his honour and his son Peadar also was in local politics as a member of Mayo County Council.