Rajendra Nath's sister Krishna married Raj Kapoor. Prithviraj Kapoor invited Rajendra Nath's elder brother Prem Nath to Mumbai. Seeing the elder brother becoming actor, Rajendra Nath also reached Mumbai in 1949. Both brothers lived together in one room. By reaching Mumbai, Rajendra Nath started his journey as a struggler and he had to face financial difficulties many times.
I.S. Johar gave Rajendra Nath the first break through 'Ham Sab Chor Hain'. The film got a great success and became the identity of Rajendra Nath. Film 'Dil Deke Dekho' directed by Nasir Hussain was the first major success of Rajendra Nath. After the success of this film, the path of struggle of Rajendra Nath became easier. In the Dev Anand and Asha Parekh's film 'Jab Pyar Kisi Se Hota Hai', Rajendra Nath got the role of playing Popat Lal. He became immensely popular in the role of Popat Lal, and he became popular with the same name among the audience.
Big and thick glasses on the eyes, cap on head, socks and big shoes, Rajendra Nath appear in many films. Their getup became extremely popular. His character often used to be a fool man. He played as idiot who acted in a straightforward way, but his actions greatly appreciated by the audience. He always cooperates with the hero and wages the villain. They were tied in this image and seen in most of the movies repeating this character. When Popat Lal's character got popularity, Rajendra Nath thought to redeem him. He made a program called 'The Popatlal Show' and presented the program abroad. This made them a lot of economic benefit.