Returning to France flat broke after military service in North Africa, Georges Duroy arrives in Paris determined to make a name for himself. Although he has no writing experience, Duroy insinuates himself into a journalist job thanks to his friend Monsieur Forestier. With the assistance of his friend’s wife, who does much of the writing, Georges gains a reputation as a journalist. Georges meets and seduces a married woman, Madame de Marelle, who helps him financially and rents an apartment for their assignations. His envious, sarcastic friends start calling him her “good friend, or “Bel-Ami.”

Meanwhile, Duroy continues his association with Madame Forestier, making an amorous advance and even suggesting, despite her refusal, that he might marry her if her husband, who is in poor health, were to die. She recommends he gain the backing of Madame Walter, the editor’s wife, which proves a good suggestion. With her support, Georges gets a promotion. When the Forestiers go to Cannes for Monsieur Forestier's health, they summon Duroy there in time to see him before he dies. Duroy immediately proposes to Madame Forestier, and they are soon married. However, it later develops that she sees him primarily as a substitute for her husband, ignoring his requests to alter her life or home in any way. At her suggestion, he changes his name to the more elegant du Roy de Cantel.

Frustrated and still very ambitious, de Cantel engages in two affairs, once again with Madame de Marelle and now with Madame Walter as well. However, his designs are on the Walters’s daughter, Suzanne, who is rich and beautiful enough for him to consider a suitable wife. Using his actual wife’s political connections, he learns of an official state financial development that is potentially worth millions. Trading on this secret information, he makes a lot of money, but the associates he tells make much more. Georges’s envy leads to a vicious double deal; he gains a divorce and ruins the government official he despises. He now marries Suzanne and contentedly contemplates his future ascent into politics. His father-in-law, understanding what kind of man he is, determines to keep a close eye on him in his new post as editor-in-chief.