[3] Early in his education at the local national primary school, his intellectual capacity and promise of greater things was often remarked upon.

[citation needed] These included James Duggan, a local Sinn Féin activist and acquaintance of Gearóid's cousin Michael Collins.

[citation needed] In 1909, O'Sullivan started at St Patrick's College of Education, in Drumcondra, Dublin, to train for a career in teaching.

A first posting was to Kildorrey, Cork in 1912, but soon transferred back to Dublin to teach at St Peter's National School, Phibsborough.

[4] It was also here that he became re-acquainted with Michael Collins, who joined the League in 1916 upon his return to Ireland from London, where he'd held a Postal Service position.

[citation needed] O'Sullivan – a Celtic studies scholar – helped Collins polish his usage of the Irish language, "to gather some extent folklore and foster literature.

Released in December 1916, he intensified his Volunteer activity with the Carlow Brigade, for which cover he retained work as a teacher at Knockbeg College.

[citation needed] O'Sullivan's appointment in 1923 as Adjutant-General had been sanctified by law in the Defence Forces (Temporary Provisions) Act.

After the war, he left the military to qualify as a barrister and build a career while spending time with his family with Maud Kiernan,[citation needed] which grew to include children Fr.

[2] In 1927, after the assassination of the then Minister for Justice Kevin O'Higgins, O'Sullivan, at the request of party leaders, contested the resulting by-election in the Dublin County on 25 August and retained the seat for Cumann na nGaedheal.

describing himself as "a colleague" wrote of O'Sullivan's contributions to Ireland following 1916:"When the jails and prison camps opened Gearoid came back to resume the struggle.

From his dingy office, within a stone's throw of Dublin Castle, surrounded by excursions and alarms, meeting places where plans for action were settled, and thence to an uneasy rest."