Pierce Mahony was born in Dublin in 1850, the family originally coming from Kerry. Mahony was to leave  his mark in Meath in the political and sporting fields.  His grandfather, Pierce Mahony, had been a close associate and solicitor to Daniel O’Connell. In 1877 he married and had two sons, Pierce Gun and Dermot Gun.

In 1881 Mahony was appointed an assistant commissioner under the Irish Land Law Act and it was his experience here that led him to support Charles Stewart Parnell and the Irish Parliamentary Party. In 1886 the sitting Member of Parliament for Meath North, Kevin O’Doherty decided to return to Australia. Parnell, who held the seat between 1875 and 1880 before successfully standing for Cork City, persuaded his friend, Pierce Mahony, to contest the election. He was selected as the party’s candidate in the Meath North constituency and was returned unopposed. As MP he took an active role in parliament. His maiden parliamentary speech in August 1886 was on the land question. In September 1886 he asked the Chief Secretary about the lack of progress in providing labourer’s cottages in Oldcastle Union. In 1889 he questioned the reason for prohibiting a meeting that was to be held in Bective Abbey to raise funds for evicted tenants. In 1891 he asked why was there a delay in hearing the case of a Ferganstown, Navan tenant who was seeking a fair rent figure.  

When the Parnell divorce crisis of 1890–91 broke Mahony was one of the small group of Irish Parliamentary Party MPs who wrote to Parnell on 28 November 1890 urging him to retire. He was one of the few to defend publicly Parnell’s marriage to Katharine O’Shea.

At the general election of 1892 Mahony stood for Meath. Michael Davitt, the noted Land Leaguer, was nominated by the Anti-Parnellites. Defeated by 54% to 46% Mahony alleged intimidation of the voters by the Catholic clergy. The inquiry into the petition was held in Trim and Mahony successfully had the result set aside. He pursued Davitt for the costs of inquiry but received nothing as Davitt was adjudicated a bankrupt. A convention of Parnellites at Trim selected Pierce Mahony to contest Meath North again. Pierce Mahony addressed a meeting at Kells on 8 January 1893  to seek amnesty for political prisoners. Mahony addressed a meeting in Oldcastle and said “that before the Home Rule Bill is accepted they must see that they have  control of all the civil forces, including the Constabulary ; the appointment of the judges. The Land Question, he thought, should be settled by a scheme of Compulsory Purchase.

Mahony contested the re-run election in February 1893 and again lost but this time by a smaller margin.

Mahony ran for parliament for various constituencies in 1895, 1915 and 1918 but was not successful. In 1900 Mahony’s financial position was secured when he inherited the Grangecon estate in co. Wicklow from an uncle, David Mahony.

When his first wife died he married his cousin, Alice,  and the newlyweds set off for Bulgaria in 1903 . Large numbers of orphans had fled the St Ilynden’s Day massacres which had occurred in the Turkish controlled Tharce and Macedonia. On 30 March 1904 he opened St Patrick’s orphanage, which continued functioning until closure during the war in 1915. Mahony took a direct interest in the welfare of the boys and indeed, for many years afterwards, the orphans adopted the name ‘Mahoni’ to honour him. Four of the orphans were brought to Ireland to continue their education. In January 1915 he received the cross of the Civil Merit from King Ferdinand I for his work in Bulgaria so he was honoured by the Kings of two opposing countries in the Great War. A street in Sofia, Bulgaria was re-named in his honour.
In 1912, on the death of his elder brother, Pierce assumed the style the O’Mahony of Kerry.

Mahony became involved in the case of the theft of the Irish Crown Jewels in 1907. His half-brother, Sir Arthur Vicars, was the Ulster King of Arms and his son, Pierce Gun  Mahony was Herald of Arms. The Irish crown Jewels consisted of  the order of St. Patrick went missing from Dublin castle. Vicars was accused of negligence. Scandalous conduct was alleged to have taken place in the castle and the true story never emerged. Mahony defended Vicars but a commission criticised him and he was removed from his position. In 1921 Vicars was assassinated and his Kerry home burned down during the troubled times and event which made Mahony vow never again to set foot in Kerry. Seven years after the disappearance of the Crown Jewels Pierce Gun Mahony was killed while climbing over a fence with a gun at Grangecon. The Crown Jewels were never recovered and the mystery never resolved.

In 1913 O’Mahony  supported the workers during the Dublin lock-out while during the war he served as a member of recruiting council. In September 1915 he visited the Leinster Regiment at the front, the Leinster’s being one of the regiments which recruited in Meath.

O’Mahony resigned as deputy lieutenant for Wicklow and from the magistracy of Kildare and Wicklow in protest against British policy in Ireland during the Anglo-Irish war. He bred Irish wolfhounds and took to wearing a kilt and having a bagpiper accompany him. In 2005 and the Irish Kilt Society held a special dinner in Dublin to commemorate Pierce O’Mahony as a noted kilt wearer. The special guest was the Bulgarian ambassador.

Pierce O’Mahony died in Wicklow in 1930. A book “Pierce O’Mahony – An Irishman in Bulgaria, ‘The O’Mahony of Kerry’ Ireland’s forgotten link with Bulgaria” by Maria Spassova and Séamus Shortall  was published in recent years.

A GAA club was formed in Navan in 1887 and it was named in honour of the local MP, Pierce Mahony. This club won the 1895 All Ireland against Arraval Rovers from Tipperary. This was the first all-Ireland to be played at Jones Road. The first game ended in a draw and in the second game Arravale were declared winners and presented with their medals. The referee reported the next day that he had recorded the scores incorrectly and Navan should have won. A new club was formed in Navan in 1948 and they chose the name “Navan O’Mahony” to commemorate the earlier club.