Simbu made his acting debut as a child artist in 1984 and acted in his father T. Rajendar’s Uravai Kaatha Kili, in which he acted in a friendly appearance.
He further acted in his father`s movies, including Thai Thangai Paasam, Oru Vasantha Geetham, En Thangai Kalyani, Enga Veetu Velan, Monisha En Monalisa, Oru Thayin Sabhatham, Samsara Sangeetham, Shanti Enathu Shanti, Pettredutha Pillai, Thiruvalla and Sabash Babu. In Samsara Sangeetham, Silambarasan danced to a song singing “I am a Little Star, Aaaven Naan Super Star”.
Silambarasan played his first protaginist role in Kadhal Azhivathillai (2002) directed by his father.The movie had a successful run. His second film was Dhum (2002), which loosely based on Jagannadh’s 2002 Kannada film Appu starring Puneet Rajkumar, had mixed reviews but a good run at the theatres. His release in 2003 was Alai,which marks the first collaboration of Simbu and Trisha, was a box office flop. This film remains the only unsuccessful film in the career of director Vikram Kumar till date.
Silambarasan had three releases in 2004. The first of three was Kovil.This film, which deals with the relationship between a Hindu boy and a Christian girl, had mixed reviews, but Simbhu was praised due to his “restraint and matured”performance. It was a box office hit. After this, Silambarasan acted in a movie called Kuththu, which is a remake of the Telugu film Dil.The movie opened with mixed reviews, but had successful run at the theatres. His final release in 2004 was Manmadhan, which had good reviews.The movie described as a good thriller. This movie has been written by himself. He also co-wrote the dialogues.
In Thotti Jaya Silambarasan played the role of an orphaned gangster who finds love. This movie was described by the critics as realistic. In 2006, he starred in Saravana, directed by K. S. Ravikumar.