The Portrait of a Lady has received critical acclaim since its first publication in The Atlantic Monthly, and it remains the most popular of James's longer fictions. Contemporary critics recognise that James had pushed the analysis of human consciousness and motivation to new levels, particularly in such passages as the famous Chapter 42, where Isabel meditates deep into the night about her marriage and the trap she seems to have fallen into. James made an in-depth account of Isabel's deepest terrors in his preface to the 1908 New York Edition of the novel.
More recent criticism has been levied by feminists. In particular, Isabel's final return to Osmond has fascinated critics, who have debated whether James sufficiently justifies this seemingly paradoxical rejection of freedom. One interpretation is: Isabel both feels as honour-bound to the promise she has made to stepdaughter Pansy as she does to her marriage to Osmond, and she believes that the scene her "unacceptable" trip to England will create with Osmond will leave her in a more justifiable position to abandon her dreadful marriage.
The extensive revisions James made for the 1908 New York Edition have generally been accepted as improvements, unlike the changes he made to other texts, such as The American or Roderick Hudson. The revision of the final scene between Isabel and Goodwood has been especially applauded. As Edward Wagenknecht noted, James "makes it as clear as any modern novelist could make it by using all the four-letter words in the dictionary that [Isabel] has been roused as never before in her life, roused in the true sense perhaps for the first time in her life." James's verbal magic allowed him to both obey and evade the restrictive conventions of his day for the treatment of sexuality in literature.
Critic Alfred Habegger has written that the main character of Portrait was inspired by Christie Archer, the protagonist from Anne Moncure Crane's novel, Reginald Archer (1871). Crane (1838–1872) may have influenced James, who Habegger considers was interested in Crane's female characters.
In the preface to the 1908 New York Edition of the novel, James referred to several of George Eliot's female protagonists as possible influences on the Portrait. Habegger questions this and quotes others as doing the same.
In another critical article, "Rewriting Misogyny: Portrait of a Lady and the Popular Fiction Debate", Paul M. Hadella also mentions the similarities with Crane.