He served as Member of Parliament (MP) in the House of Commons of the United Kingdom of Great Britain and Ireland representing Mid-Cork from 1901 to 1918,[1] a constituency comprising the districts of Ahadallane, Ballincollig, Ballyvourney, Blarney, Coachford, Farran, Inchigeelagh, Macroom, Millstreet and Shandangan.

After he married in 1894, he moved in pursuit of journalistic experience temporarily to Scotland where in 1896 he joined the staff of the Glasgow Observer, then becoming London editor of the Catholic News in Preston, England.

In the towns and in the country, labourers had to live in hovels and mud-wall cabins which bred death and disease, huddled together in indiscriminate wretchedness, landless and starving, the last word in pitiful rags and bare bones.

The grant of Local Government and the extension of the franchise, enabled the labourers to eventually take a mighty stride in the assertion of their independent claims.

The Irish Party leadership refused to consider direct Parliamentary representation to the Land and Labour Association, an indication of the middle-class determination with maintaining its hold over national politics.

[19] Following the death of Dr C. K. D. Tanner (former Mid-Cork anti-Parnellite Nationalist MP from 1895), a United Irish League selection convention was called for 10 May 1901 in Macroom to decide between three candidates for the up-coming by-election.

Standing as ILLA candidate on a solely labour platform, "D. D.", as he was popularly known, defeated the official local Irish Parliamentary Party (IPP) candidate Cornelelius O'Callaghan of Millstreet after a second ballot, amidst turbulent and occasionally violent scenes following an initial attempt by Joseph Devlin (representing the UIL National Directory), to exclude a number of ILLA branches from the convention.

[20] Sheehan was carried triumphantly from the venue and when finally returned as MP in the by-election of 17 May,[1] he wrote: Aged twenty-eight, he was the youngest, and one of the most outspoken, Irish nationalist party members of parliament at the House of Commons.

In his capacity as honorary secretary of the Cork Advisory Committee, he was foremost in ending centuries of oppressive "landlordism" under the far reaching Wyndham Land Purchase Act of 1903.

[6] At countrywide ILLA meetings and in leading articles and editorials,[35] Sheehan strove vigorously to attain betterment for the working Irish as in his June 1904 Commons speech on the Labourers (Ireland) Bill.

Together with O'Brien under the "Macroom programme"[36] their unabated pressure helped win passage of the exceptional Bryce Labourers (Ireland) Act (1906), remarkable its financial features for state sponsored rural housing,[37] several provisions of which Sheehan suggested and drafted.

The dwellings provided homes for over 60,000 landless labourers and their families, comprising a rural population of a quarter of a million previously living wretchedly, mostly together with their livestock, in one room stone cabins and sod hovels.

[38] Within a few years the resulting changes heralded an unprecedented socio-economic agrarian revolution in rural Ireland, with widespread decline of rampant tuberculosis, typhoid and scarlet fever.

[45] Subsequently, together with D. D. Sheehan as its organising honorary secretary, William O'Brien then inaugurated his new political movement, the All-for-Ireland League (AFIL) in Kanturk, March 1909.

[46] The League was a distinctively new political group whose deep conviction was that the success of a United Ireland parliament must depend on Irish Home Rule being won with the consent rather than by the compulsion of the Protestant minority.

[47] Prophetically farsighted, both Sheehan and O'Brien advocated granting Ulster every conceivable concession to overcome its fears of a Catholic-dominated Dublin parliament, as otherwise an All-Ireland settlement would fail.

[50] Opposed by the official IPP+UIL+AOH nominee William Fallon in the 24 January 1910 general election, as well as denounced by Catholic clerics for pitting labourer against farmer,[51] he was returned with 2824 votes against 1999 for his opponent.

[1] Sheehan later commented on the contest: I was left to fight my battle almost single handed, having arrayed against me two canons of my Church, and every Catholic clergyman in the constituency, with two or three notable exceptions.

Sheehan campaigned for the AFIL's policies at large meetings across counties Cork and Limerick, in Mayo together with O'Brien – coming under revolver fire at Crossmolina – their party generally handicapped by lack of clerical support.

Trained at Buttevant barracks County Cork, gazetted lieutenant, he practically raised the 9th (Service) Battalion of the Royal Munster Fusiliers, a regiment of the 16th (Irish) Division.

Receiving Captaincy and Company command in July 1915, he served with the 2nd RMF Battalion along the Loos salient in France under Irish Major General William Hickie.

Hospitalised often, he was decommissioned late 1917, with a bulletin stating that he "relinquished his commission on account of ill-health contracted on active service, and is granted the permanent honorary rank of Captain, 13 Jan.1918".

The AFIL members, seeing their political concepts for an All-Ireland settlement displaced by the path of militant physical-force, recognised the futility of contesting the December 1918 general elections.

In the changed political climate strongly opposed to Sheehan's earlier army service and recruiting, and faced with intimidation,[6] he and his family left their Cork city home and moved to England.

[67] During the Commons debate in October 1918 on the Irish Land (Provision for Soldiers) Bill, in the course of a lengthy speech Sheehan said: With an election demand of "Land for fighters"[69] aimed at returned ex-servicemen, Sheehan contested in December the United Kingdom general election as adopted Labour Party candidate for the Limehouse division of Stepney in London's East End and polled 2,470 votes second to the returned Liberal,[70] over a million demobilised servicemen still in Europe were unfortunately unable to vote.

He rigorously demanded national de-rating for farmers and objected to the County Council "manager system", proposing instead the establishment of separate independent coastal Boroughs north and south of Dublin.

The thing is too absurd and ridiculous for words, yet it is those puerile arguments that are being trotted out again and again by those who never spared the art of lying and wilful perversion when dealing with Irishmen of the Great War.

[74]Controversial themes continued to be highlighted during 1930 in the Dublin Chronicle, particularly when calling for freedom of speech after the "disgraceful breaking up" of the new Labour Party's inaugural meeting on 8 April in the Mansion House by organised gangs of Fianna Fáil and Peadar O'Donnell followers shouting "Up de Valera" and "Up Devlin".

Sheehan finished mid-field in the list of candidates, his housing campaign hijacked by the larger party rivals Fianna Fáil and Cumann na nGaedheal.

From the 1930s, unable to practise in court due to impaired hearing from the war, as advocate Sheehan provided legal advice and assistance to former constituents, to help them defend against claims on their right to security of tenure and ownership entitlements of their lands, granted under earlier legislation.