After his father's (Roshan Lal Nagrath) untimely death, Roshan started his career as an assistant director to film maker Mohan Kumar in films like Anjaana starring Rajendra Kumar and Babita. Actor Rajendra Kumar referred him to some film makers and thus he was signed by Soodesh Kumar for Man Mandir starring Sanjeev Kumar and Waheeda Rehman. But he made his entry as an actor, making his debut in the 1970 film Ghar Ghar Ki Kahani, in which he got a supporting role. He got very few solo hero films in his career. He got solo hero roles in more women-oriented films where the focus was more on the heroine, such as Paraya Dhan with Hema Malini, Aankh Micholi with Bharati, Khubsoorat with Rekha and Kaamchor with Jaya Prada. His few successful solo hero films, with the focus equally on both hero and heroine, were Aankhon Aankhon Mein with Rakhee, Nafrat with Yogita Bali, Ek Kunwari Ek Kunwara with Leena Chandavarkar, Hamari Bahu Alka with Bindiya Goswami and Shubh Kaamna with Rati Agnihotri. J. Om Prakash produced Aankhon Aankhon Mein with Rakesh in the lead. Later, J. Om Prakash directed Aakraman, with Sanjeev Kumar in the lead, and had Rakesh in a supporting role, and then produced Aakhir Kyun?, with Rajesh Khanna in the lead and Rakesh in a supporting role. Rakesh played supporting roles in a few successful films such as Man Mandir with Sanjeev Kumar in the lead, Khel Khel Mein with Rishi Kapoor in the lead, Bullet with Dev Anand as the hero, Hatyara with Vinod Khanna in the lead, Dhongee with Randhir Kapoor, Khandaan with Jeetendra and Neeyat with Shashi Kapoor as the lead hero. He played supporting roles regularly in films with Rajesh Khanna in the lead role and of those, Chalta Purza was a failure and the other three were blockbusters - Dhanwan, Awaaz and Aakhir Kyon?. The few multi-star cast films he was part of as the lead hero that were successful between 1977 and 1986 were Devata, Shriman Shrimati and Haathkadi, all of which had Sanjeev Kumar as the main lead hero and Jaag Utha Insan and Ek Aur Sikander, which had Mithun Chakraborty in the main lead, and other hits such as Dil Aur Deewaar, Khatta Meetha, Unees-Bees (1980) and Maqaar (1986). Most of his other films as second lead hero or solo hero films between 1973 and 1990 were box office flops.