Anbu Thozhi movie opens with a simpleton from a small village in Tamil Nadu wanting to become a musician in the Tamil film industry. The role played by debutant Prabhu (Prabhu) goes to Chennai in search of his dream career where he meets Pandya (Mayil Samy).
Pandya helps Prabhu into the big city life and they become good friends. Prabhu meets Yazhini (Preethi Verma) who helps him meet a famous Director, who gives Prabhu a chance to prove his music skills.
On becoming a successful man, Prabhu finds love in Yazhini who helped him achieve his dream. When Prabhu decides to reveal his feelings for Yazhini, she breaks the news about Karuppu (Thirumavalavan) who helped her many years ago when she was abandoned as a child during the war and also helped her reach India.
Yazhini requests Prabhu to go find and talk to Karuppu about her love for Karuppu. Prabhu hides his love and sets off to find Karuppu. On meeting Karuppu, Prabhu realizes that he is a man for the country which he is fighting for and that he has no room in his heart for any individual human soul. His country was his life.
Prabhu returns home a confused man and tells Yazhini that Karuppu also was in love with her and that he will soon come to marry her. Confusions grow as Prabhu's mother comes to Chennai to meet her future daughter in law. Pandya reveals the truth about Karuppu to everybody and Yazhini realizes that by waiting for Karuppu (who will never come) she is not giving life its true meaning.
The film closes with Yazhini and Prabhu getting together.