Ajit’s father strongly emphasised education and wanted his son to focus solely on his studies. However, according to Ajit’s son Shahzad Khan, young Hamid defied his father, sold his schoolbooks, and ran away to Bombay (now Mumbai). During his early struggle, he spent nights sleeping inside cement pipes, often harassed by local gangsters demanding protection money. Ajit faced these threats with sheer physical strength, eventually earning their respect and emerging as a local hero.

He began his acting career in the 1940s, initially working as an extra in films. Although he later secured lead roles, success eluded him. On filmmaker Nanabhai Bhatt's advice, he adopted the screen name Ajit, meaning indomitable, as ‘Hamid Ali Khan’ was considered to be too lengthy. At the urging of his friend Rajendra Kumar Tuli, Ajit agreed to take on roles of the villain. Kumar was instrumental in getting Ajit the antagonist's role in 'Suraj', where he himself was in the leading role.

From there on, Ajit redefined cinematic villainy, delivering memorable performances in films such as 'Zanjeer', 'Yaadon Ki Baraat' and 'Kalicharan'. Ajit became legendary for his iconic dialogues like “Mona Darling…", “Lilly, don’t be silly" and “Saara shehar mujhe Lion ke naam se jaanta hai“, which remain etched in the Bollywood culture. Some of his other notable films include 'Naya Daur', 'Nastik' (based on the Partition ), 'Shikari', 'Mughal-e-Azam', 'Bara Dari', 'Opera House', 'Halaku' and 'Anand Math'. Over a career spanning nearly four decades, Ajit shared the screen with stalwarts as Prithviraj Kapoor, Dilip Kumar, Dev Anand, Shammi Kapoor, Dharmendra, Amitabh Bachchan.

It is often noted with admiration that nearly every song picturised on Ajit, or featuring his presence became an all-time hit, even when the films themselves were not major successes. These timeless songs include “Yeh Desh Hai Veer Jawano Ka", “Bhula Nahin Dena Ji", “Dekho Mausam Kya Bahaar Hai", “Main Khushnaseeb Hoon", “Aaja Ke Intezaar Mein", “Dil Ka Na Karna Aitbaar Koi", “Yeh Haseen Raat Yeh Bahaar Yeh Sama", “Zindagi Bhar Gham Judaai Ka" and poet Pradeep’s powerful “Dekh Tere Sansaar Ki Haalat“.

Ajit acted in over 200 films, predominantly portraying a sophisticated and stylish villain. Despite playing ruthless gangsters, his onscreen persona was marked by elegance, calm authority and refined mannerisms. He was often seen in bold checkered suits, wide sunglasses and striking jewellery, with his female accomplice frequently addressed as “Mona." He rarely engaged in violence himself, instead commanding a loyal gang of secondary villains - often played by actors like Jeevan, Ranjeet and Kader Khan, typically bearing westernised names like Peter, Michael or Robert.

Ajit retired from films in 1981 following a heart bypass surgery. He passed away on October 22, 1998 in Hyderabad. He is remembered as one of the most iconic villains in Indian cinema. His contemporaries included Amrish Puri, Amjad Khan, Ranjeet and Prem Chopra. Ajit introduced a new style of villainy - soft-spoken, composed, and yet intensely commanding - that set a lasting benchmark in Bollywood.