His best-known performances as a comedian were in Aag (1948) and Awaara (1951), where he played the younger version of the characters played by his older brother Raj Kapoor and in Sangram (1950), where he played the younger version of Ashok Kumar and Dana Paani (1953) where he acted with Bharat Bhushan. He worked in four Hindi films as a child artist from 1948 to 1954.
Shashi Kapoor trained couples with Raakhee, Sharmila Tagore and Zeenat Aman from the late sixties to the mid-eighties. He has also played with actresses Hema Malini, Parveen Babi and Moushumi Chatterjee in numerous films. After their first film together, Sharmelee became a blockbuster, Raakhee was often associated with him, and they played in hit movies such as Jaanwar Aur Insaan (1972), Kabhi Kabhie (1976), Baseraa (1981), Trishna acclaimed by the Critical (1978) however, Doosara Aadmi (1977), Bandhan Kuchchey Dhaagon Ka (1983), Bandh Honth (1984) and Zameen Aasmaan (1985) were flops.  He played with Sharmila Tagore in such hits as Waqt (1965), Aamne Samne (1967), Suhana Safar (1970), Aa Gale Lag Jaa (1973), Vachan (1974),  Paap Aur Punya (1974), Swati (1986), the critically acclaimed New Delhi Times (1985), who won Kapoor's National Film Award for Best Actor in 1986,  Other Films with Sharmila, such as My Love (1970) Anari (1975), Gehri Chot (1983), Maa Beti (1986) and Ghar Bazar (1998) were unsuccessful.
With Zeenat Aman, he has worked in such successful films as Chori Mera Kaam (1975), Deewaangee (1976), Roti Kapda Aur Makan (1974), Heeralal Pannalal (1978), Pakhandi (1984), Bhavani Junction (1985) , Satyam Shivam Sundaram (1978) and the pair witnessed flops such as Krodhi (1981), Vakil Babu (1982) and Bandhan Kuchchey Dhaagon Ka (1983). He made 10 films in front of Hema Malini. As a pair, Shashi and Hema Malini have had 6 hits such as Abhinetri, Aap Beati, Trishul, Aandhi Toofan, Apna Khoon, Maan Gaye Ustaad, Do Aur Do Paanch and 3 flops - Jahan Pyar Mile, Naach Uthe Sansaar and Anjaam.
He has accepted very few roles as an actor in films since 1987. He played with Pierce Brosnan in The Deceivers (1988).Shashi Kapoor asked Amitabh Bachchan to play in her ambitious debut film, Ajooba. Amitabh Bachchan agreed to make the film because of her friendship with Shashi Kapoor, although at the time Amitabh was not signing any new films.
The film did not do very well at the box office in India, but was ranked as a hit abroad. The film had a sumptuous budget with a mega star. The film over the years has been appreciated for its tales and roles of Amitabh Bachchan, Rishi Kapoor, Shammi Kapoor and Amrish Puri.
He also won a national award (special jury) for his performance in the 1993 film In Custody and played Rajah in the television adaptation of Gulliver's Travels (1996).
Kapoor was admitted to Kokilaben Hospital, Versova, Mumbai, on December 4, 2017, for a chest infection,  where he died of cirrhosis of the liver at the age of 79 years at 17:20, according to the Kokilaben Hospital as confirmed at the Press Trust of India (PTI).His nephew Randhir Kapoor confirmed the news. Kapoor is survived by two sons, Kunal and Karan, and a daughter, Sanjana, who takes care of the Prithvi theater.