Thomas Fowler is a middle-aged English journalist stationed in Vietnam to report on the war between French colonial forces and the Viet Minh. He professes a cynical, detached worldview, preferring to observe the violence rather than participate in it. He maintains a sexual relationship with a young Vietnamese woman named Phuong and relies on her to prepare his opium pipes. Despite his insistence on strict neutrality, his comfortable routine is disrupted by the arrival of an idealistic American.

Alden Pyle is an earnest, young American working as an economic attaché in Saigon. He studies academic textbooks by York Harding and believes Vietnam needs a "Third Force" to establish democracy. Pyle approaches the dangerous war zone with a bright optimism that irritates older expatriates. He quickly becomes infatuated with Phuong, approaching Fowler directly to announce his intentions to marry her and offer her a life in the United States.

Phuong is a young Vietnamese woman living with Thomas Fowler in Saigon. She possesses practical ambitions, desiring financial security and a reliable way to escape the violence of her home country. She rarely discloses her inner emotions, allowing the foreign men in her life to project their own desires onto her. She enjoys looking at pictures of the British royal family and American landmarks, viewing both countries as potential escape routes.

Miss Hei is Phuong's older sister. She speaks excellent English and actively manages her sister's romantic prospects. Viewing Fowler as a poor match due to his existing marriage, she strictly evaluates other men to secure her sister's financial future. She later uses her language skills to secure a job at the American Legation.

Vigot is a French police inspector stationed in Saigon. He frequently questions Fowler about incidents in the city and occasionally plays dice with him. He reads the philosophy of Blaise Pascal and approaches his police duties with a weary acceptance of the ongoing war and the sheer volume of casualties.

Helen is Thomas Fowler's wife, who lives in England. She is a devout Catholic who communicates with Fowler exclusively through letters. She understands her husband's habit of abandoning women and acts as a vocal critic of his choices, initially refusing to grant him a divorce on religious and moral grounds.

Joe is an overweight, disheveled American economic attaché. He works alongside Pyle in Saigon and hints to Fowler that the young man's duties extend far beyond standard economic matters. He eventually hires Miss Hei to work at the American Legation.

Bill Granger is a brash American correspondent covering the war in Vietnam. He prefers to spend his time drinking heavily and visiting brothels rather than discussing political nuances. He covers French military press conferences in Hanoi and uses his boisterous attitude to mask private family troubles back home.

Mr. Heng is the manager at a Chinese warehouse owned by Mr. Chou. He holds communist sympathies and acts as a quiet informant for Fowler. He points the journalist toward American manufacturing materials being used in the conflict, attempting to guide Fowler out of his strict neutrality.

General Thé is a military leader operating independently in Vietnam. He commands a private army fighting against both the French colonial forces and the communist Viet Minh. He becomes a subject of intense interest for foreign agents seeking to establish a new political faction in the country.

Captain Trouin is a French bomber pilot. He takes Fowler on a military raid, dropping napalm on ground targets. He later visits an opium den with Fowler, where he confesses his guilt over the civilian casualties caused by his missions and the brutal reality of fighting for the crumbling French empire.

Dominguez is Thomas Fowler's assistant in Saigon. He gathers information from the local community and directs Fowler toward potential news stories, including rumors about the American trade office's activities.