He was born in 1884 in Kiltyclogher, Co Leitrim. At the age of 16 he emigrated to Glasgow where he initially obtained work as a gardener. Leter he worked as a tram conductor.
By 1902 he had moved to Belfast and had obtained work as a barman. He joined the Celtic League and there met Bulmer Hobson (Irish Republican Brotherhood) who asked him to become an organiser for the Dungannon Clubs, set up to promote the IRB in Ulster.
In 1906 he joined the Belfast circle of the IRB and was later appointed treasurer of the IRB’s supreme council. He became a close friend of Tom Clarke and was appointed manager of the IRB publication Irish Freedom.
In 1910 MacDermott became a full-time organiser for Arthur Griffith’s Sinn Féin. He spent the next few years travelling the country setting up party branches and organising for the IRB, which was his real mission.
In 1912 he was crippled by an attack of polio but he continued his work. Probably the most popular of the senior IRB activists, he was elected to the provisional committee of the Irish Volunteers in 1913 and in 1915 became a member of the military council set up by the IRB to plan the Rising.
He fought in the GPO in the 1916 Rising and was subsequently executed on May 12th, 1916.
Poem about Sean MacDermott
Composed By Phil McGovern (U.S.) & Recited By Michael (McFetty) McGovern
Brave Leitrim Sons & Daughters
Around Lough Allen Shore
From Drumshambo town to Mohill
Kinlough to Ballinamore
They assembled in their thousands
On Last Saint Patrick’s Day
And Their Cheers Should Reach Old Erin
As they march in their parade
It was the picture on the banner
That aroused the ring and cheer
Some men that bowed their heads in prayer
Some women shed a tear
For it was their martyr Sean Mac Dermott
On their banner they portrayed
To lead Leitrim sons & daughters
In their Saint Patrick’s Day parade
He bore the scares of battle
As they marched him out to die
His comrade Commandant Connolly
On a stretcher there did lie
They raised Connolly’s wounded body
So the soldiers might take aim
As the bullet pierced his noble heart
While helpless there he lay
I hope their souls in heaven now rest
Free from all earthly care
And with the good saint Patrick
Their heavenly bliss they share
On earth they’re not forgotten
Never shall their memory fade
May their spirit’s lead those yet unborn
On Saint Patrick’s Day parade