In the subsequent Irish Civil War, he was targeted for assassination by anti-Treaty forces and was shot and badly wounded in Dublin in December 1922.

He was critical of the proposed Irish Boundary Commission and resigned from Cumann na nGaedheal and founded a new political party called Clann Éireann in 1926.

[3] On each of these occasions he was subjected to a smear campaign by his former party colleagues who used his pro-Treaty stance during the civil war against him.

It was alleged that he had personally selected his fellow county man Liam Mellows for execution.

In fact, Mellows was executed in reprisal for the attack on Ó Máille and Sean Hales in 1922.