Although unconnected with the Easter Rising in 1916, McNeill was arrested and jailed by the British Dublin Castle administration.

He served as a member of the committee under Michael Collins, the chairman of the Provisional Government, that drafted the Constitution of the Irish Free State.

[citation needed] However, McNeill's tact was not reciprocated by de Valera's government, and some of its ministers sought to humiliate McNeill as the King's representative by withdrawing the Irish Army's band from playing at functions he attended and demanding he withdraw invitations to visitors to meet him.

In one notorious incident in April, two ministers, Seán T. O'Kelly (a future President of Ireland) and Frank Aiken, publicly walked out of a diplomatic function when McNeill, there as the guest of the French ambassador, arrived.

[1] In June 1932, John Charles McQuaid, President of Blackrock College, hosted an extravagant garden party to welcome Papal Legate Cardinal Lorenzo Lauri, who had arrived in Ireland to represent Pope Pius XI at the 31st International Eucharistic Congress.