[2] During 1920 and 1921, Kennedy was a senior legal adviser to the representatives of Dáil Éireann during the negotiations for the Anglo-Irish Treaty.

He was highly regarded as a lawyer by Michael Collins, who later regretted that Kennedy had not been part of the delegation sent to London in 1921, to negotiate the terms of the treaty.

[3] On 31 January 1922, Kennedy became the first Attorney General in the Provisional Government of the Irish Free State.

The functions of the Provisional Government were transferred to the Executive Council of the Irish Free State.

[4] The results were not always happy: his diary, of which some extracts have been published, reveal the increasingly unhappy atmosphere in the Supreme Court itself, due to frequent clashes between Kennedy and his colleague Gerald Fitzgibbon, since the two men proved to be so different in temperament and political outlook that they found it almost impossible to work together harmoniously.

[7] He was also a delegate of the Irish Free State to the Fourth Assembly of the League of Nations, between 3 and 29 September 1923.

He was elected to Dáil Éireann on 27 October 1923, as a Cumann na nGaedheal TD at a by-election in the Dublin South constituency.

Kennedy campaigned for the replacement of the wigs and gowns traditionally worn by judges and barristers, which he regarded as the trappings of an alien regime.