Mac Diarmada (MacDermott), Seán (1883–1916), republican revolutionary, was born January 1883 (baptised 29 January) in Corranmore (Laghty Barr), Kiltyclogher, Co. Leitrim, eighth child and third son among five sons and five daughters of Donald McDermott (d. 1913), a carpenter, and Mary McDermott (née McMorrow) (d. 1892), native of the nearby townland of Ardmoneen (Loughros Barr). Educated at Corracloona national school, he studied by correspondence course for a king's scholarship to train as a teacher, but twice failed the examination owing to deficiency at mathematics. After working briefly and unhappily as a gardener in Edinburgh (1904), he studied bookkeeping, shorthand, and Irish at a night school near Dowra, Co. Cavan, and was deeply influenced by his teacher's nationalism (winter 1904–5). Moving to Belfast, he worked as a tramcar conductor (1905–6), until his dismissal for smoking on a tram platform.
The relentless organiser Involved for a time in the Ancient Order of Hibernians (AOH), he soon converted to militant, physical-force republicanism. Joining a Dungannon club (1905), he met members of the secret Irish Republican Brotherhood (IRB), one of whom, victim of the purge of inactive members being conducted within the organisation's Belfast circle by Bulmer Hobson (qv) and Denis McCullough (qv), recommended Mac Diarmada as his replacement. Sworn into the IRB (1906), he joined eagerly in the reinvigoration of the body's Belfast organisation. Appointed full-time organiser, with a bicycle and small salary, of the Dungannon Clubs – the open organisation founded by Hobson and McCullough to promote republicanism in Ulster – he especially sought recruits from the AOH, exacerbating the considerable ill feeling between the rival bodies. When the Dungannon Clubs amalgamated with the Cumann na nGaedheal organisation of Arthur Griffith (qv) to form the Sinn Féin League (April 1907), Mac Diarmada became an organiser for the new body, founding local branches initially throughout Ulster and then nationally (1907–11). He canvassed extensively in the 1907–8 North Leitrim parliamentary by-election campaign waged for Sinn Féin by Charles Dolan (qv).
At the instigation of McCullough, who was co-opted to the IRB supreme council in 1908, Mac Diarmada was appointed the brotherhood's national organiser (1908–16). He moved with Hobson to Dublin, where they allied with IRB veteran Thomas Clarke (qv), recently returned from America, in urging a more active policy upon the semi-moribund organisation, and undermining the authority of the body's old-guard national leadership. Physically robust and gregarious, Mac Diarmada toured the country tirelessly by foot or bicycle or motorcar, engaged in the open activity of organising Sinn Féin clubs, and the clandestine activity of recruiting likely men into the IRB, thus weaving a vast web of personal contacts throughout Ireland. He was the chief operative implementing the IRB policy of infiltrating national cultural organisations, and placing IRB men in leadership positions within them. He himself was active in Dublin in the Gaelic League, the GAA (as a non-playing club member), a GAA pipe band, and the Celtic Literary Society. From 1908 he organised the annual Aonach na Nollag, a Christmas exhibition of Irish goods sponsored by Sinn Féin to promote development of native industries. He was manager of the monthly journal Irish Freedom (November 1910–December 1914), an initiative of McCullough and Clarke launched under the cover of the Dublin Wolfe Tone Clubs committee, and intended to express IRB opinion. Through 1910–12 the contest between IRB militants and moderates centred on first the launch, and then the control, of the newspaper, concluding in resignations of key old-guard leaders. During this time Mac Diarmada succeeded John MacBride (qv) as Connacht representative on the IRB supreme council (probably 1911).
In autumn 1911 Mac Diarmada was stricken with poliomyelitis; hospitalised for several months, and convalescing subsequently in the homes of friends, he was rendered partially disabled in the right leg (among other lasting chronic complications), and thereafter walked with a limp and the aid of a stick. He travelled to the USA as IRB delegate to the Clan na Gael convention in Atlantic City, New Jersey (October 1912), where he propounded the organisation's new activist philosophy and programme. From as early as 1911 he promoted the profile within republican circles of Patrick Pearse (qv), recognising his potential value to the movement despite the initial guardedness of Clarke and others.
Conspiring for insurrection Elected secretary of the IRB supreme council (1913), Mac Diarmada constituted, with Clarke (treasurer) and James Deakin (qv) (president), the body's standing executive, empowered under the brotherhood's constitution to act for the supreme council between meetings. With Deakin distracted by business commitments, Clarke and Mac Diarmada exercised the powers of the executive to impose their policy upon the entire organisation, increasingly concentrating governance of the IRB into their hands alone. Among several top IRB activists involved in the launch of the Irish Volunteers, Mac Diarmada attended the initial organising meeting in Wynn's hotel (11 November 1913), and addressed one of the two overflow meetings at the paramilitary body's public launch in the Rotunda (25 November 1913), at which he was elected to the provisional committee. Perceiving with Clarke the Volunteers’ potential as an IRB-controlled army capable of staging an armed rebellion, as a paid Volunteer organiser he established units countrywide while continuing his IRB recruitment, placing members of the secret organisation into key Volunteer commands. The controversy over co-option of nominees of John Redmond (qv) to the Volunteers’ provisional committee (June 1914) caused Mac Diarmada's and Clarke's bitter and lasting estrangement from Hobson, who had agreed to Redmond's demand to avoid a split in the movement. During the Howth gun-running (26 July 1914) Mac Diarmada operated together with Clarke in a hired taxi as scouts for the Volunteer column returning with arms through Clontarf to Dublin, and conveyed several loads of rifles in the taxi to safe locations.
Instrumental in the decision of the IRB supreme council to stage an armed rising during the first world war, he joined Clarke in convening the secret meeting representing the spectrum of advanced nationalist leadership in the Gaelic League library, Parnell Square, that resolved to pursue that objective (9 September 1914). Over the ensuing winter the pair allowed the advisory military committee formed at the meeting to lapse, determining to confine planning for the rising within a much smaller, trusted, and more tightly controlled clique to obviate potential betrayal by informers and spies. Mac Diarmada was among the twenty members of the Volunteers’ provisional committee who signed a statement (24 September 1914) repudiating Redmond's speech at Woodenbridge, Co. Wicklow, which pledged support to Britain in the first world war. The ensuing Volunteers’ split paradoxically enhanced his and Clarke's designs, by placing at their disposal a smaller, more militant, and more easily manipulated paramilitary organisation. Mac Diarmada was elected to the Irish Volunteers’ general council at the body's first convention (October 1914), and to the central executive at the second convention (October 1915). After government suppression of Irish Freedom for its anti-war line (December 1914), Mac Diarmada was manager and registered owner of the new IRB organ, Nationality (1915–16). He was imprisoned for four months in Mountjoy jail (May–September 1915) after making a vigorous anti-recruiting speech to a Volunteer meeting at Tuam, Co. Galway.
On his release he and Clarke joined the secret military council – already consisting of Pearse, Joseph Plunkett (qv), and Éamon Ceannt (qv) – assembled by Clarke during Mac Diarmada's imprisonment to devise the detailed plans for the rebellion. Amid a concurrent reorganisation of the IRB supreme council, Mac Diarmada engineered the election of the Belfast-based McCullough as president, thereby securing his and Clarke's unimpeded control of the executive. At its last meeting prior to Easter Week (January 1916), the supreme council approved Mac Diarmada's motion for a rising at the earliest possible date, and sanctioned the existence of the military council. Mac Diarmada was prominent in initiating and conducting the discussions with James Connolly (qv) that resulted in the latter's approval of the plans for the rising and his co-option to the military council (January 1916), which subsequently co-opted Thomas MacDonagh (qv) as a seventh member.
The Easter rising Throughout the early months of 1916 Mac Diarmada was at the centre of the final logistical preparations for the rising. His role in the confused events immediately preceding the rising was critical. He and Plunkett most likely instigated circulation of the ‘Castle document,‘ a purported leak suggesting an imminent government move to disarm the Volunteers, which conveniently supplied a plausible cover before the eyes of the Volunteers’ moderate leadership for the final mobilisation activity. On Good Friday morning (20 April) Mac Diarmada persuaded Volunteer commander-in-chief Eoin MacNeill (qv), who had learned the previous evening of the plan to rise on the Sunday, that the insurrection should proceed because the expected arrival of German arms made likely a government move to suppress the movement, but also increased the prospects for success. Mac Diarmada ordered the temporary detention of Hobson that evening, fearing his interference with the conspirators’ intentions. When MacNeill learned on the Saturday of the loss of the arms ship and arrest of Roger Casement (qv), and was made aware of the extensive subterfuges of Mac Diarmada and his fellow conspirators, he reversed his position and issued an order countermanding the Volunteers’ scheduled Easter manoeuvres. Mac Diarmada secured the military council's decision on Sunday morning (23 April) (against Clarke's wish to proceed as planned) to delay the rising by one day, to allow time to rescind the countermand.
As a member of the provisional government into which the military council now transformed itself, Mac Diarmada signed the proclamation of the republic. Throughout the rebellion he remained, in civilian clothes, with the headquarters garrison in the General Post Office, functioning as adjutant to Connolly (the commander-in-chief), and coordinating the operation of a field hospital in the building. From the Thursday evening, as Connolly weakened from wounds, Mac Diarmada and Clarke, though neither held officers’ rank in the Volunteers, increasingly commanded the direction of the battle. Mac Diarmada ordered evacuation of the wounded to Jervis Street hospital on the Friday, and amid the confused evacuation of the burning GPO, rallied the troops to continue the manoeuvre in the face of withering hostile fire. With Pearse in military custody after agreeing to surrender on Saturday afternoon (29 April), Mac Diarmada read the surrender order to the garrison in the new headquarters in a Moore St. shop, adding his own commendation of their gallantry. With calm logic, he quelled a section of the garrison who wished to fight on, stressing their duty to survive the rebellion, so as to some day ‘finish the job’.
Among the party of prisoners held overnight outside the Rotunda hospital, and ridiculed for his disability by the officer-in-charge who confiscated his walking stick, the next day he was conducted to Richmond barracks under a slower escort separate from the main column of prisoners. After escaping identification by intelligence agents for some days, at his court-martial (9 May) he conducted a spirited defence, challenging prosecution evidence, cross-examining witnesses, and demanding that all allegations against him be proved. Found guilty of participation in armed rebellion, he was acquitted on a lesser charge of causing disaffection among the populace. He and the severely wounded Connolly were the last two of the rebellion leaders to be executed by firing squad in the yard of Kilmainham jail (12 May), despite growing public disquiet, and protests by British and Irish politicians (both nationalist and unionist).
Assessment Mac Diarmada's historical legacy is inseparable from that of Tom Clarke, his closest friend and political ally; as Clarke was the master mind behind the Easter rising, Mac Diarmada was the master machinist, the man who more than any other assembled and manipulated the various cogs of organisation. In the last critical months of planning and plotting, it was Mac Diarmada, with his genius for covert activity and intrigue, network of personal contacts, and comprehensive knowledge of the strength, calibre, and leadership of individual IRB and Volunteer units countrywide, who wielded the greater control over events, concealing certain of his machinations even from Clarke himself. His obsession with secrecy, perceived as essential to obviate informers, undermined the communications necessary to stage successful insurrection.
Ideologically a pure physical-force separatist, single-mindedly devoted to expelling British government from Ireland, he was hostile toward trade-unionism and socialist internationalism as impeding the development of native entrepreneurial industry and diluting national feeling. Dark-haired and handsome, he was an articulate and persuasive public speaker. His foremost asset as a revolutionary intriguer was said to be the simple and warm charm of his manner, which attracted and instilled confidence among a wide diversity of personalities. His example was cited by Michael Collins (qv) as the model for the latter's post-1916 reorganisation of the IRB and strategic exploitation of the secret society as a personal power base in the conduct of armed insurrection.
Unmarried, from 1915 Mac Diarmada was romantically attached to Josephine Mary (‘Min’) Ryan, a Cumann na mBan activist and NUI graduate from a prosperous farming background in Tomcool, Co. Wexford, who later married Richard Mulcahy (qv); Min and her sister were the last visitors prior to Mac Diarmada's execution. His brother Séamus MacDermott (1887–1962) emigrated to America (1914), was active there in Clan na Gael and the New York branch of the Irish Volunteers, and joined the staff of the Gaelic American, succeeding on the death of John Devoy (qv) as the paper's editor (1928–62). A statue of Mac Diarmada was unveiled in Kiltyclogher (1940). The family homestead and cottage in Corranmore, purchased by the state in 1964, is a national monument under the OPW. The rail station in Sligo town and a street in Dublin city centre bear Mac Diarmada's name.