He grew up attending school at Mountrath Monastery and St Patrick's College, in Carlow, Ireland.

In April 1895, O'Kelly was elected as a Member of Parliament as an Anti-Parnellite Irish National Federation candidate at the by-election for the East Wicklow constituency, following the resignation of John Sweetman MP.

[2] Instead, O'Kelly focused on local politics, becoming the first chairman of the newly established Wicklow County Council in 1899.

In 1910, O'Kelly returned to the House of Commons as the Member of Parliament (MP) representing West Wicklow, having been elected unopposed at a March 1910 by-election to fill the vacancy caused by the death of James O'Connor.

O'Kelly was a close friend of Douglas Hyde, first President of Ireland, and John Redmond, a leader of the Irish Parliamentary Party.