Rowland Mallet, a wealthy Bostonian bachelor and art connoisseur, visits his cousin Cecilia in Northampton, Massachusetts, before leaving for Europe. There he sees a Grecian figure he thinks a remarkable work of art. Cecilia introduces him to the local sculptor, Roderick Hudson, a young law student who sculpts in his spare time. Mallet—who loves art but is without artistic talent himself—sees an opportunity to contribute: he offers to advance Roderick a sum of money against future works which will allow Roderick to join him in moving to Italy for two years. Mallet believes that in Rome, Roderick will be exposed to the kind of artistic influences which will allow his natural talent to fully mature. Roderick is galvanized by the offer, but he fears his highly protective mother's disapproval and urges Mallet to meet with and reassure her. Mallet does so, eventually overcoming the woman's doubts. At the meeting, Mallet is also introduced to Mary Garland, a distant poor cousin of the Hudsons who has been living with them as a companion to Mrs. Hudson. Mallet finds himself unexpectedly attracted to the young woman—to her simplicity, her lack of affectation, her honesty. During a farewell picnic attended by many of the Hudsons' friends and family, Mallet realizes he has fallen in love for the first time in his life. But, because of his natural reserve and imminent departure for two years, he fails to declare his feelings, yet still harbors hopes that something may yet come of the relationship.
That hope is crushed when, on the voyage across the Atlantic, Roderick reveals that just before leaving he asked Miss Garland to marry him and she accepted. "...You came and put me into such ridiculous good-humor," Roderick tells Mallet, "that I felt an extraordinary desire to tell some woman that I adored her." Mallet listens to all this with the feeling that fortune has played an elaborately-devised trick on him; that just as he had finally found love, it had been stolen away because of his own act of generosity.
After a rough start in Rome, Roderick begins to flourish in the arts community, building a reputation as an original talent and a charming, if ill-mannered, character. Meanwhile Mallet attempts to suppress his feelings for Mary Garland by cultivating a relationship with Augusta Blanchard, another expatriate American artist living in Italy. When Roderick decides to visit Switzerland or Germany, Mallet travels with him part way before going on to visit friends in England. There Mallet writes to Mrs Hudson to inform her of the situation. She replies saying she is pleased the situation has gone so well. However, when Rowland finally hears from Roderick, he begs him for money to cover the debts he incurred while gambling at Baden-Baden.
The two men return to Rome where, one fateful day, Christina Light enters Roderick's studio to peruse his artwork. Christina has grown up on the Continent, tended by her ambitious mother and the mother's aging Italian escort, the Cavaliere. She is, by general agreement, one of the most startlingly beautiful young women in Europe, and her mother is determined to marry Christina to a wealthy and titled gentleman. The impoverished Roderick is nonetheless instantly infatuated with Christina, eventually obtaining approval to sculpt her bust and thereby ingratiating himself with the family. Although the prematurely world-weary Christina professes not to like Roderick, she admires his bluntness. Mallet finds himself in a wrenching emotional bind – attempting to prevent Roderick from consummating his love with Christina so as to protect Mary Garland from emotional injury; knowing all the while that doing so will foreclose forever any possibility that he himself can marry the only woman he has ever loved.
Later Mallet encounters Christina and Roderick at the Colisseum. He saves Roderick from falling to his death attempting to catch an out-of-reach flower for Christina. Mallet subsequently happens to meet Christina alone and urges her to give up her flirtation with Roderick, revealing to her that Roderick is engaged.
Rowland writes a letter to Cecilia about Roderick's fall. Later Roderick decides not to complete his sculpture for Mr Leavenworth, leading Rowland to be annoyed with him. Rowland visits Madame Grandoni and meets Christina there. He then decides to leave for Florence, but decides to make up with Roderick and bring his mother and his betrothed over to Italy to save him. While doing some sightseeing, Miss Garland admits to being afraid of changing. They walk into Christina and Roderick says she might not marry the Prince after all.
Roderick then does a sculpture of his mother. Mrs Hudson thinks she owes something to Rowland for all he has done. Upon completing the bust, Roderick says he will not marry Miss Garland. Rowland and Gloriani witness another of Roderick's tantrums. Later, Mrs Grandoni says Miss Blanchard is marrying Mr Leavenworth, although she is in love with Rowland. She then throws a party and Christina turns up uninvited to observe Miss Garland and be vituperative. The next day the latter admits she takes Christina to be fake. Later after the Prince has left, the Cavaliere visits Rowland and entreats him to advise Christina, as she has no father to turn to. After checking on Roderick because his mother has received a note from him saying he didn't want to be disturbed, he goes to the Lights' and talks to Christina. She says she doesn't like the Prince but likes Roderick as a friend. She has however married the Prince...
Roderick admits to his mother he is unable to work and is crippled with debts. Upon Rowland's counsel, they move to cheaper accommodation in Florence. When his morale isn't improving, his mother suggests moving back to Northampton, Massachusetts. Instead, Rowland persuades them to move to Switzerland. There, he seems a little closer to Miss Garland; Rowland asks him about Christina, but he avoids the question. Later, they walk into Sam; then Rowland chances upon Christina and the Prince; Roderick comes along and he is stupefied with her beauty. He then wants to join her in Interlaken as she has asked of him. He begs Rowland, his mother, and Miss Garland for money. Rowland admits that he is in love with Miss Garland. Finally, Roderick dies in a storm while on his way to Interlaken; Rowland and Sam find his dead body the next day. Mrs Hudson and Miss Garland return to Massachusetts.