When Winston Churchill attacked Irish taoiseach Éamon de Valera 70 years ago at the end of the second world war for what he regarded as southern Ireland’s shameful neutrality, De Valera responded in a dignified and firm way. Irish neutrality was the logical culmination of De Valera’s mission to achieve Irish sovereignty, and as far as he was concerned the capacity to implement an independent foreign policy was the ultimate measure of that sovereignty. That he had managed to guide southern Ireland to that point was testament to his political success, nearly 20 years after Churchill, as secretary of state for the colonies, had suggested De Valera “may gradually come to personify not a cause but a catastrophe”.

Despite the deep-rooted antagonism between the two wartime leaders, they had much in common. Both had extraordinary political longevity, made spectacular comebacks after political defeat and humiliation and felt they were walking with destiny. This book explains why and how De Valera managed his political journey and how he exercised, sometimes abused and skilfully retained power over the course of a public career that lasted an astonishing 60 years.

It might be legitimately asked if there is a need for another biography of De Valera given the abundance of existing ones. Perhaps there is not, and there is nothing hugely revelatory in these pages, but what Fanning has done is more than worthwhile; this is a succinct distillation of much of the existing literature on De Valera, combined with Fanning’s own insights and judgments as a veteran historian of Irish politics. It is stylishly written, accessible, full of clarity and mature assessments, and makes judicious use of De Valera’s private correspondence. It also convincingly challenges some of the narrow castigations of De Valera as a hysterical anglophobe.

Fanning characterises him as “incomparably the most eminent of Irish statesmen”, who could generate “near absolute obedience”, and who in the 1930s rewrote “almost single-handedly the constitutional relationship between Britain and Ireland”. But Fanning’s De Valera is no plaster saint; he was “deeply conservative” and spoke to political colleagues “in a manner reminiscent of a schoolmaster talking to a class of dim pupils”. He was economically illiterate, and during the Irish civil war “plumbed the depths of anti-democratic contempt for majority rule” and made “grotesquely irresponsible” interventions that did enormous damage.

The sole surviving commandant of 1916’s Easter Rising, where as a military leader he demonstrated ineptitude and indecisiveness, he escaped execution because he was relatively unknown. Subsequently elected to lead the Irish republican movement, he spent 18 months of the Irish war of independence in the US where he raised $6m but did not win official recognition of the Irish republic. Nonetheless it was an important sojourn; he was out of tune with the IRA campaign at home and on his return sought to alter its direction, demonstrating what became a consistent reluctance “to share collegial authority within the cabinet”. As moves towards a truce with Britain intensified, he badly miscalculated. His Anglo-Irish strategy at that stage was based on the belief that he could forge a third way between dominion status and an Irish republic: “swaddled in the comfort blanket of four years of deference and obedience, De Valera tried to chart a course too subtle to be understood by those less intellectually astute than he was”.

He was not against compromise, but he refused to be a part of the Irish delegation that negotiated the Anglo-Irish treaty of December 1921. His arrogant rationale was that he, as “the symbol of the Republic should be left untouched”. But such loftiness backfired. He adamantly opposed the treaty offering dominion status because it was not his compromise. As the majority backed the treaty, he was sidelined by hardline republicans and had to carve a path back to power, which he did in a very effective and focused way, leading Fianna Fáil, the party he established in 1926.

He went on to win power in 1932 and dominated Irish politics for the next two decades before serving two terms as Irish president. His greatest achievement in the 1930s was to maximise Irish sovereignty by essentially winning the trust of British politicians and diplomats and then ripping up the pages of the Anglo-Irish treaty, removing the British crown from Irish affairs and moulding a constitution that in 1937 made southern Ireland a republic in all but name. He crushed the IRA, kept Ireland out of the second world war and audaciously and self-righteously visited the German ambassador in Dublin in 1945 to express condolences on the death of Hitler.

What he could not do – and this is why he did not declare an Irish republic – was come up with a means to end the partition of Ireland; he settled instead on rhetorically beating the anti-partition drum and relying on what became “his well-worn and plaintive theme of British culpability”. He declared in the Irish parliament in 1935 in relation to ending partition: “We have no plan.” This remained the case. De Valera’s vision, Fanning concludes, was “powerful but blinkered”. The skill and confidence he brought to the successful quest for sovereignty, however, leads Fanning to assert that he can be seen as the essential man in the making of the modern Irish state. He was “ever pedantic” with that, and a divisive character because of the route he took, but as Churchill was to discover, he did it with a dignity and resoluteness that deservedly secured for him an elevated place in the history of Irish nationalism.

Diarmaid Ferriter is professor of modern Irish history at University College Dublin. His most recent book, A Nation and Not a Rabble: The Irish Revolution 1913-23, is published by Profile.

Éamon de Valera: A Will to Power is published by Faber (£20). Click here to order a copy for £16