At seventeen O’Connor leaves school to become a stonemason. In October 1893, at the age of 23, he goes to Boston, where he stays five years. On his return to Ireland, he moves to Dublin, where he soon establishes himself as a “speculative builder” constructing houses in Anglesea Road, Dolphin’s Barn, Eglington Road, Brendan Road, and Donnybrook.
O’Connor joins the Gaelic League in 1900, through which he comes into contact with many of the future leaders of the Independence movement, including Tom Clarke and Seán Mac Diarmada. He is sworn into the Irish Republican Brotherhood (IRB) in 1909 and enrolls in the Irish Volunteers in 1913, the same night as Éamon de Valera.
While not directly involved during the Easter Rising, O’Connor is recognised and arrested on his return to Dublin and sent to Kilmainham Gaol, then to Richmond Barracks, Wandsworth Prison, and finally to Frongoch internment camp, in North Wales.
On his release in September 1916, O’Connor re-establishes his business and takes up his political activities. He reconnects with members of the Keating Branch of the Gaelic League at 46 Parnell Square, and takes part in the re-organising of the fragmented IRB. He canvasses for by-elections in Kilkenny and Armagh on behalf of Sinn Féin candidates W. T. Cosgrave and Patrick McCartan.
O’Connor is involved with the revolutionary Sinn Féin party during the time of the First Dáil, handling money and hiding documents for Michael Collins. He purchases 76 Harcourt Street for Michael Collins, following a raid on the Sinn Féin Office at No. 6. There he installs a secret recess for private papers and means of escape through the skylight. When the recess escapes discovery following a raid, he goes on to construct hiding places in many of the other houses used by the movement. He is one of the shareholders of the National Land Bank which is set up in March 1920 at 68 Lower Leeson Street.
O’Connor plays a role in the “National Loan,” raised by Collins to fund the fledgling Dáil Éireann. The loan, which had been declared illegal, is lodged in the individual bank accounts of the trustees. The gold is kept under the floor of O’Connor’s house until 1922.
O’Connor takes the pro-Treaty side during the subsequent split over the Anglo-Irish Treaty. He is an unsuccessful candidate for Dáil Éireann at the 1923 general election, in the Dublin County constituency.
After the death in November 1923 of Cumann na nGaedheal TD Michael Derham, O’Connor is the Cumann na nGaedheal candidate at the Dublin County by-election on March 19, 1924, when he is elected to the 4th Dáil ahead of Seán MacEntee. He retains his seat at the next four general elections, joining Fine Gael when Cumann na nGaedheal merges in 1933 with the National Centre Party and the Blueshirts. He serves as a Trustee of Cumann na nGaedheal.
After his death on February 7, 1935, the 1935 Dublin County by-election is won by Cecil Lavery of Fine Gael.