Kapoor started his career as an assistant director, and made his acting debut with the MF Hussain 2004 film Meenaxi: A Tale of Three Cities.

Following a career breakthrough with Rang De Basanti (2006), Kapoor went onto appear in ‘’Aaja Nachle’’, ‘’Laaga Chunari mein daag’’ in (2007), Bachna Ae Haseeno (2008), Welcome to Sajjanpur (2008), Don 2 (2011), Luv Shuv Tey Chicken Khurana (2012), Dear Zindagi (2016), Veeram (2016), Gold (2018) After a break, Kapoor earned critical acclaim for his portrayal of Babur, in The Empire (2021).

Along with his acting career, Kapoor is a writer, entrepreneur and co-founder of Ketto, Asia’s largest crowdfunding platform.

He began his career as an assistant director of Aks,[1] Kapoor made his acting debut playing Kameshwar, a car mechanic, opposite Tabu in Meenaxi: A Tale of Three Cities, which was helmed by painter MF Hussain and released in 2004.

Ronjita Kulkarni of Rediff.com termed him "a pleasant surprise" and added, "His freshness adds appeal to his character, yet he emotes like a seasoned actor.

"[2] In 2006, Kapoor had his breakthrough with Rakeysh Omprakash Mehra's Rang De Basanti, where he played a college student who after a tragedy, fights against corruption with his friends.

Firstly, he played a cricket obsessed man in Hattrick alongside Rimi Sen. Yash Raj Films subsequently signed Kapoor for a three-film contract, two of which released in the same year.

Alongside Huma Qureshi, he played a Omi, who desire to go to London but is forced to move back home.

[15] Live Mint's Sanjukta Sharma stated, "Kapoor is not the cynosure, but he pulls off the silliness and sensitivity of Omi’s character capably.

[19] Sweta Kaushal of Hindustan Times noted, "Kunal Kapoor, gets an edge among the youngsters and essays his part with finesse.

[23] Tigmanshu Dhulia's Raag Desh, based on the Indian National Army trials was Kapoor only release in 2017.

He played Shah Nawaz Khan, and Saibal Chatterjee of NDTV stated that Kapoor delivered a "steady performance".

[26] Devesh Sharma of Filmfare noted, "Kunal Kapoor as the strict coach lend gravitas.

His first release was Koi Jaane Na, opposite Amyra Dastur, where he played Kabir, a writer and vigilante.

[33] Vibha Maru of India Today praised Kapoor and noted, "The actor breathes life into the character of Babur.

"[34] While Pradeep Menon of Firstpost added, "Kunal cuts an impressive figure as Babur, but he is caricatures at the end of the day.

"[41] In 2009, Kapoor started writing weekly columns for HT City, the lifestyle supplement of the Hindustan Times.

He co-founded Asia's largest crowdfunding platform called Ketto,[45] which raises money for social and individual causes.