Ip Man is set in the 1930s in Foshan, a hub of Southern Chinese martial arts, where various schools actively recruit disciples and compete against each other. Although the Wing Chun master Ip Man is the most skilled martial artist in Foshan, he is unassuming and keeps a low profile. As an independently wealthy man, he feels no need to accept any disciples and instead spends his days training, meeting with friends, and spending time with his family. However, his wife is often resentful of the time he spends training and discussing martial arts with friends and colleagues. Though not a professional martial artist, Ip is respected in Foshan due to the abilities he displays in friendly, closed-door competitions with local masters. Ip's reputation is further enhanced when he defeats an aggressive, rude, highly skilled Northern Chinese martial arts master, Jin Shanzhao, thus upholding the regional pride of fellow Southern stylists and others in Foshan.
The Japanese invasion in 1937 adversely affects the life of everyone in Foshan. Ip's house is claimed by the Japanese and used as their Foshan headquarters. Ip and his family lose their wealth and are forced to move into a decrepit house. Desperate to support his family, Ip accepts work as a coolie at a coal mine. The Japanese General Miura, who is a Karate master, establishes an arena where Chinese martial artists compete with his military trainees. The Chinese earn a bag of rice for every match they win. Li Zhao, a former police officer and Ip's acquaintance, is now working as a translator for the Japanese and is making the offer to the martial artists working as coolies. Ip at first declines to participate in the matches. However, when his friend Lin goes missing, he agrees to take part in order to investigate. He is enraged when he sees a fellow Foshan master (Master Liu) mercilessly executed for picking up a bag of rice from a prior victory after giving up in a second match against three karateka. He also comes to understand that Lin was killed in an earlier fight. Barely able to contain his rage, Ip demands a match with ten karateka at once. Despite having not practiced Wing Chun since the invasion began (in order to conserve what little food his family had to survive), he proceeds to mercilessly crush each of them with a brutal barrage of his martial art mastery, showing none of the restraint he exhibited in previous engagements. His skill arouses the interest of Miura, who seeks to learn more about Ip and see him fight again.
Ip visits his friend Chow Ching-chuen, who owns and runs a cotton mill in Foshan. Chow tells Ip that a highway robbery gang led by Jin Shanzhao is harassing his workers and trying to extort money from them. Ip trains the workers in Wing Chun for self-defense. Meanwhile, Miura grows impatient when Ip does not return to the arena and sends men to find him, prompting Ip to incapacitate them and go into hiding with his family at Li Zhao's house. Meanwhile, the robbers return to the cotton mill to demand money. The workers fight back using the techniques that Ip taught them, but Ip appears to take care of things personally and defeats Jin Shanzhao, warning him never to harass the workers again.
The Japanese soldiers eventually find Ip at the cotton mill. Miura tells Ip that his life will be spared if he agrees to instruct the Japanese soldiers in martial arts. Ip refuses and challenges Miura to a match, which Miura accepts, both because of his love for martial arts and because refusing the challenge would be a humiliation to the Japanese. The match between Ip and Miura is held in public in Foshan's square. At first, the two fighters seem equally matched, but Miura soon finds himself unable to penetrate Ip's impeccable defense and becomes overwhelmed by his relentless and direct blows. He is helpless to defend himself as Ip effortlessly uses him as a Wooden Dummy, inflicting a severe beating on him and clearly winning.
As the beaten general lies down after his defeat, Ip looks over to the cheering Chinese crowd and spots his wife and child with Chow. Suddenly, Miura's deputy Sato shoots Ip, sparking a scuffle between the Chinese audience and the Japanese soldiers. During the scuffle, Li Zhao kills Sato with Sato's own gun. Ip is taken away amidst the chaos. It is revealed that he survives and escapes to Hong Kong with his family. There, Ip establishes a Wing Chun school, where his students come to learn martial arts from him, including Bruce Lee.