How was Ireland able to maintain neutrality during WWII, while other British dominions (like Canada) were immediately brought into the war effort?

Simply put, Britain didn’t have the power or influence in Ireland to bring them into the war and the Irish government was particularly anti-British compared to other Dominions

The Long version: Just before the First World War, there was a movement in Ireland demanding Home Rule that was agreed to by Britain, but delayed in 1914 due to the start of the war. Because of the political situation, of which Home Rule was only part, the British Gov decided not to implement conscription in Ireland but did encourage the Irish Volunteers, a predecessor to the original IRA, to volunteer willingly to join the British army.

The Irish Volunteers split as many went off to France, while some of the Volunteers who stayed in Ireland held an uprising in Dublin known as the 1916 Rising. There was a heavy-handed response to the Rising by the Brits with many of the leaders of the Rising executed, and this caused a shift away from Ireland demanding Home Rule to demanding full independence.

Irish people who joined the British army during WW1 were also ostracised and shamed when they returned. My hometown didn’t put up a memorial to those who died until this year.

Following the 1918 UK election (in which Sinn Fein, the Irish Nationalist party, won a majority in Ireland) the ‘Old’ IRA began a war of independence that lasted until 1922 with the signing of the Anglo-Irish treaty, granting the ‘Irish Free State’ dominion status (Northern Ireland remains part of the UK) as well as allowing Britain to keep a few naval bases, among other things.

The Old IRA split again into the Pro-Treaty IRA, which became the Irish Army, and the Anti-Treaty IRA, who wanted to keep fighting for full independence and to reclaim the North. This started a civil war that lasted until 1923.

In 1932 Eamonn De Valera, the original President of Ireland during the war of independence and the leader of the anti-treaty IRA during the civil war, was elected as the official leader of the Irish Free State. He pretty much immediately went to work stripping the Free-State constitution of any ties with Britain and tried to dislodge Ireland as a British subject. Part of this was starting a trade-war with Britain, and when that ended in 1938, Britain relinquished control of its ports in Ireland. By 1939 Britain had no military capacity in Ireland.

The Irish Free State had also made a bit of an impact in international politics, with a key part of that being a commitment to neutrality. De Valera was leader of the League of Nations in the lead up to WW2

When WW2 broke out, Britain knew that they couldn’t force Ireland to join the war, and too much pressure to join would lead to possibly creating an enemy-friendly nation on their doorstep. Churchill offered De Valera Northern Ireland at one stage in return for Ireland joining the war, but De Valera refused as he didn’t think Churchill would fulfil his promise.

In Ireland, WW2 is known as ‘The Emergency’. Although they remained neutral, they weren’t completely neutral. Ireland interned members of the IRA, who had links to Nazi Germany hoping to get guns and support for another rebellion. German pilots who landed in Ireland were interned as well (although there is an interesting story of a German spy who landed in the wrong place in full uniform, was given directions by the local police, and lived out the rest of the war outside Dublin), while Allied pilots were smuggled back to the UK.

De Valera retained some political ties to Germany. Controversially, upon hearing of Hitlers suicide, De Valera sent the German ambassador a letter expressing his sympathies.

TLDR: Ireland didn’t want to join the war and wouldn’t give in to pressure from Britain to join, and Britain had known they couldn’t force them to join since before 1914

Hope that answers your question in a sort of roundabout way!