Given the fame he and his work have enjoyed for the past half century, it is extraordinary that no full-length study on Paul Henry has appeared until now.

Many of this artist's paintings have achieved iconic status as idealised representations of Ireland, helping to create an enduring image of the country in the popular imagination.

It is, therefore, fascinating to discover just how tough were Henry's circumstances for much of his professional life and how hard it was for him to find buyers for the pictures now so widely admired.

S B Kennedy's newly-published and generously illustrated biography of Paul Henry has been many years in preparation and is unlikely to be supplanted by any other work for an even longer period. The author is especially good at untangling the complications of the painter's personal life and the consequences of this on his art.

In contrast to the serenity apparent in the west of Ireland views for which he has become famous, Henry's first marriage was a stormy affair. His wife Grace, a fine artist whose work is also given generous attention by Kennedy, was eight years older than Paul Henry and prone to live far beyond the couple's means. Her husband was, for many years, expected to pay for the bills she ran up in Ireland, England and France; at one stage, Henry considered placing a notice in the national newspapers declaring he would no longer be responsible for his wife's debts, but was persuaded against this course of action.

The combination of marital discord with an extravagant wife and relatively poor sales of his pictures inevitably had an effect on Henry, making him increasingly inclined to paint what he knew would find an audience.

And yet, even the Connemara pictures for which he eventually became most widely known and appreciated took time to achieve widespread popularity. In these works, the human figure which had been central to Henry's paintings during the first decades of the 20th century, almost entirely disappeared. Instead, from the early 1920s onwards, landscape and sky became competing leitmotifs as the canvas was horizontally divided between the two. Only the inclusion of cottages and piles of cut turf provide evidence of people in Henry's pictures during the later decades of his career. Typical of such work is Connemara, painted in 1924-5 and reproduced on a widely-distributed tourism poster issued by the London Midland and Scottish Railway Company.

Here the lowering sky and towering mountains dwarf the cluster of whitewashed and thatched cottages shown in an otherwise unspoilt landscape. As Kennedy correctly attests, "by over-popularising his treatment of the western landscape, to the extent that he became a prisoner of his own success", a painting like Connemara, which was used for advertising purposes, "marked the onset of a decline in the quality of his work from which, although arrested from time to time, he never fully recovered."

Here The Irish Times is quoted from August 1925 declaring that "if thousands of people in Great Britain and in America have been led this summer to think over the claims of Ireland as holiday ground, it is largely through the lure of Mr Paul Henry's glowing landscape of a Connemara scene."

It was, just as importantly, to the detriment of Henry's own art that these glowing landscapes - conveying as they did the impression of a remote, unspoilt and timeless Ireland - would come to seem the summation of his work and the early pictures he produced during and immediately after his time on Achill Island would be so little remembered. Because, delightful while the later work may be as a sequence of scenic backdrops, it has little of the authority, both emotional and aesthetic, evident in such powerful canvases as The Potato Diggers of 1910-11 or the same period's Launching the Curragh. These are the pictorial equivalent of Synge's plays as poetic expressions of the very difficult lives led by the population of the west of Ireland and Paul Henry's reputation with later generations will depend on them.

Paul Henry by S B Kennedy is published by Yale University Press, price £30 sterling.