While still in high school, Philip visited the set of the film The Thief of Bagdad, where he met Douglas Fairbanks. Fairbanks offered young Philip a screen test, and then a part in the movie. But when Philip rushed home to tell his mother, she refused to allow him to become an actor, saying "No son of mine is going to get mixed up with those awful people."

Ahn graduated from school in 1923, and went to work in the rice fields around Colusa, California. The field was owned by the Hung Sa Dan, or Young Korean Academy, a Korean independence movement which trained young Koreans to become leaders of their country once it became free from Japanese rule. Because Koreans could not own land, the Academy used Philip's American citizenship and put the property in his name. But because of heavy rains, the rice crops failed, and Philip found himself deep in debt not of his own making.

Philip's father was in Asia working for independence, so the younger Ahn had to support his mother and four younger siblings. He worked as an elevator operator in Los Angeles. In 1934 Philip began attending the University of Southern California. Although he was interested in the import-export business, a conversation with his father, who told him that if he really wanted to be an actor he had to commit to being the best actor he could be, convinced him to begin taking acting and cinematography courses. While in school he appeared in a stage production of Merrily We Roll Along, which toured in the Western United States.

While still in college, Philip served as president of the Cosmopolitan Club, chairman of the All University Committee on International Relations, and assistant to the dean of men, as advisor for foreign student affairs. Philip was responsible for organizing visits by many foreign dignitaries, including Princess Der Ling of China, Indian journalist Chaman Lal and archeologist-explorer Robert B. Stacey-Judd. Following his sophomore year, however, Philip dropped out of school to pursue acting full time.

Philip's first film was A Scream in the Night in 1935. He appeared in the Bing Crosby film Anything Goes the following year, although director Lewis Milestone had initially rejected him because his English was too good for the part. He appeared in many other films in this period, including Klondike Annie, The General Died at Dawn, The Good Earth, Thank You, Mr. Moto, Charlie Chan in Honolulu, King of Chinatown and Daughter of Shanghai.

Ahn starred opposite Anna May Wong in the last two films, leading to gossip that the two would marry, but they never did. He later starred in The Story of Dr. Wassell and Stowaway, opposite Shirley Temple.

During the war years, he played many Japanese characters in various war films. Because of the violent hatred of Japanese during the war, many movie viewers sent him death threats. Partly in order to counter the image of him as an evil Japanese soldier, Philip Ahn joined the United States Army, but he was forced out because of a bad ankle. During his brief time in the Army, he served in Special Services, entertaining troops.

Following the war, Ahn appeared in Love Is a Many-Splendored Thing, Around the World in Eighty Days, Thoroughly Modern Millie and Paradise, Hawaiian Style, with Elvis Presley. In the 1950s, he opened a Chinese restaurant with his sister, Soorah. "Phil Ahn's Moongate Restaurant" was one of the first Chinese restaurants in the San Fernando Valley, and existed for over thirty years before finally closing.

Ahn was always involved in the Korean community of Los Angeles. He worked hard to make Los Angeles a sister city of Pusan, Korea. He also helped to bring the Korean Friendship Bell to San Pedro. The Bell has been seen in many subsequent movies. He served as honorary mayor of Panorama City for twenty years.

In 1968, Ahn made a USO tour of Vietnam, visiting both American and Korean troops throughout South Vietnam.

Ahn's last major role was that of "Master Kan" in the television series Kung Fu. A life-long Presbyterian, Ahn felt that the Buddhist homilies his character quoted did not contradict his own personal religious philosophy.

Philip worked to have his father and mother buried together in Seoul. His father had been buried far from the city because the Japanese hoped to play down his independence work. His mother had died in California. They had not seen each other from the time Dosan returned to Korea in 1926, before the birth of his youngest son. Working with the Korean government, Ahn helped to establish a park to celebrate his father's worth, and was able to have his parents buried there, together.

Philip Ahn has a star on the Hollywood Walk of Fame.

Philip's younger brother, Philson Ahn,and had a small acting career as well. He was best known as "Prince Tallen" in the twelve-episode serial Buck Rogers with Buster Crabbe.