He wanted to become a playback singer but destiny made him an ace director of his time. He had learned classical music from the age of six, and as a student, had joined All India Radio, filling in whenever a singer could not make it. He struggled hard to become a singer, only one composer gave him a song that too after rehearsing went to Mukesh. He did get a song in 1949 film Bhool Bhulaiya, Bulo C Rani composed it, later in Madan Mohan's debut film Ankhen (1950), wherein he sang the quaint 'Rail Mein Jeeya Mora'.
During his struggle days, he became a friend to Dev Anand, who spotted his talent of direction made him an assistant of Guru Dutt at the time of making of Baazi in 1950. He assisted Guru Dutt in Jaal(1952) and Aar Paar(1954).
in 1954 got a break with "Milap", starring Dev Anand and Geeta Bali. In this film, not only Raj Khosla made a debut as a Director, but a new Music Director, N. Dutta gave debut music. The next film he directed was C I D (1956) which was a hit From here onwards he never looked back. His next two films Kala Pani (1958) and Solva Saal (1958) were back to bach hit.
He entered into production also, he co-produced and directed Bombay Ka Babu which was again a hit. Till then he directed 5 films in all the 5 films Dev Anand was his hero. The next film he directed was Ek Musafir Ek Hasina in 1962 for Shashdhar Mukharjee with Joy Mukharjee as a hero. The next film he directed was Woh Kaun Thi (1964) with Manoj Kumar and Sadhana.
Khosla explored a variety of styles be it crime thrillers like CID, suspense thrillers like Woh Kaun Thi, and musicals (Ek Musafir Ek Hasina (1962). Now he tried melodramas (Do Badan (1966) , he was successful in that too. In 1969 he came out with Do Raste and Chirag both the films were hit. The next genre he tried dacoity with highly successful Mera Gaon Mera Desh in 1971 and Kachhe Dhaage in 1973.
He made films after Mera Gaon Mera Desh and had hits like Prem Kahani (1975) starring the then hottest pair of the day Rajesh Khanna and Mumtaz, Nehle Pe Dehla (1976) and Main Tulsi Tere Aangan Ki (1978). After enjoying big hits like Main Tulsi Tere Aangan Ki (1978) and Dostana (1980) with Amitabh Bachchan, Zeenat Aman, and Shatrughan Sinha, Khosla ran into some rough weather as his other films started flopping. The last film he directed was Sunny in 1984, which was not a hit.A dispirited Khosla took refuge in alcohol and died in Bombay on 9 June 1991
He, along with Guru Dutt and Vijay Anand, was among the directors, who were also responsible for song picturizations being taken to a new high in the Hindi cinema of the 1950s and 6os.
Songs were sung by Raj Khosla in films