Walshe returned to Ireland where he studied at Mungret College, County Limerick, and began teaching at the prestigious Jesuit-run boarding school of Clongowes Wood.
While the Irish War of Independence continued, Walshe worked with Ó Ceallaigh and his small team for international recognition of the nascent government of which he was now an employee, and which the British authorities considered illegal.
Robert Brennan, who was Under-Secretary for Foreign Affairs prior to the split, and who sided with the anti-treaty faction, recommended to the pro-treaty George Gavan Duffy that Walshe would be a capable replacement for him to organise the Department.
[2]: 18 Gavan Duffy accepted the recommendation of his erstwhile colleague and Walshe was appointed Acting Secretary of the Department of Foreign Affairs of the Provisional Government.
On 2 May 1945, he and Taoiseach Éamon de Valera visited Hempel at home in Dún Laoghaire to express the Irish Government's official condolences on the suicide of Adolf Hitler.