Few architects have made a greater impact on Dublin than James Gandon, the subject of a new biography by Hugo Duffy. What will strike any reader is how much Gandon's presence in Ireland was a matter of happy chance rather than design.

He was almost 40 when he arrived in Dublin, and his career in England before that time had been rather undistinguished, with barely a handful of completed commissions to his name. It is interesting to discover that he was offered the opportunity to work in St Petersburg in 1779, two years before coming to Dublin, but declined. Instead, the Scottish architect, Charles Cameron, went to Russia and left as decisive a mark on its capital as Gandon was to on Dublin.

Even before moving to the city in April, 1781, Gandon had already established links with Ireland. At the age of 16, he had gone to work for Sir William Chambers, the architect responsible for Lord Charlemont's Marino Casino in Dublin; Gandon may have had a hand in the plans for this building. In the late 1760s, he had been awarded second place in a competition to design Dublin's new Royal Exchange (now City Hall), the first prize going to Thomas Cooley. Gandon's drawings for the building have been lost but Hugo Duffy offers a reconstruction of the work which suggests a more severe structure than Cooley's, which is currently being restored.

Even with Gandon's connections with Charlemont and his friends, his move to Ireland still seems surprising and is due to the patronage of the Hon John Beresford, the driving force behind plans to build a new custom house in Dublin. The old building used for this purpose was considerably further up the Liffey by Capel Street Bridge and because ships needed to dock there, it was impossible to throw a bridge across the river linking Sackville Street (now O'Connell Street) with the city's southside. Such a bridge would greatly assist the work of Beresford's brother-in-law, the property developer Luke Gardiner, who was responsible for laying out new streets in north-east Dublin.

This helps to explain why the new custom house site was so far down river and why Beresford and his friends were so determined to succeed, even though the land on which they wished to build was then little more than marsh. In addition, a vigorous campaign had to be waged against the merchants of Dublin who were perfectly happy with the existing arrangements and saw no advantage in building a custom house far from where they were used to conducting business.

Throughout 1781, a hostile press campaign was organised against both Beresford and his architect but this eventually proved unsuccessful.

Having succeeded in winning the commission for the custom house, Gandon then went on to snatch almost every major architectural job offered in Dublin over the next 20 years. Among the most important of these undertakings was the Four Courts, Carlisle (now O'Connell) Bridge, the House of Lords extension and the King's Inns.

The opposition he experienced is understandable under these circumstances, since no other architect appeared to have any chance of finding major work while Gandon was in Ireland. And yet, his career here ended almost as suddenly as it had begun. In 1805, at the age of 63, Gandon retired and moved to a property he owned in Lucan. Although he lived for 18 more years, he never worked again.

Architectural historian Maurice Craig has noted that all of Gandon's major work has been bombarded, burnt, rebuilt or added to - most of them this century - and it is, therefore, impossible to see anything by this architect exactly as he would have wished. Nevertheless, the external forms of his finest work remain and they are among the most important buildings in Dublin, those which give the city its distinguishing character.

Had Gandon not come to Ireland, it is probable that such buildings would have been erected because the leading politicians and businessmen of the period were determined to embellish their capital. But credit deserves to go to John Beresford for spotting Gandon's ability and bringing him to Dublin where his architectural talents were given an opportunity never permitted them in his native England.

James Gandon and his Times, by Hugo Duffy, is published by Gandon Editions and costs £25.