By the late 1940s, Ramamoorthy joined C. R. Subburaman's South Indian film-music ensemble and met fellow violinist T. G. Lingappa.
[3] Composer and singer C. S. Jayaraman commissioned Viswanathan–Ramamoorthy for Ratha Kanneer's background music, writing the songs himself.
They had a flair for light, sweet melodies, and 1950s films such as Porter Kandan, Paasavalai, Thenali Raman, Gulebakavali, Sugam Enge and Sorgavasal attracted attention.
The Hindi song "Laut gaya gam ka zamana", sung by Lata Mangeshkar and Hemanta Kumar Mukhopadhyay, copies the duo's Telugu song Teeyani Eenati Reyi (sung by P. Susheela and G. K. Venkatesh) and was a hit in the north.
During the late 1950s, Viswanathan–Ramamoorthy composed for musical hits such as Pudhaiyal, Nichaya Thaamboolam, Padhi Bhakti and Bhaaga Pirivinai.
After a 1961 disagreement with his composer, A. M. Rajah, C. V. Sridhar commissioned Viswanathan–Ramamoorthy for his films and Gemini Studios and AVM Productions later engaged the duo.
At this time, they were assisted by R. Govardhanam, G. K. Venkatesh, Shankar–Ganesh and Henry Daniel and used Pattom Sadan for vocal and sound effects.
During their early years, they worked with established male singers such as Thiruchi Loganathan, C. S. Jayaraman, S. C. Krishnan, Ghantasala and V. N. Sundaram.
The singing actors N. S. Krishnan, T. A. Madhuram, V. Nagayya, T. R. Mahalingam, K. R. Ramasamy, J. P. Chandrababu, P. Bhanumathi and S. Varalakshmi also sang for the duo.
P. Leela, Seerkazhi Govindarajan, Udutha Sarojini, K. Jamuna Rani, M. S. Rajeswari and A. L. Raghavan owe their 1950s and 1960s vocal success primarily to the duo, particularly to Viswanathan.
On 16 June 1963, Viswanathan and Ramamoorthy were given the title of Mellisai Mannargal (Tamil: மெல்லிசை மன்னர்கள், Kings of Light Music) by Sivaji Ganesan at a Madras Triplicane Cultural Academy ceremony sponsored by T. M. Ramachandran, director C. V. Sridhar and Chitralaya Gobu of the Hindu Group of Publications.
In 1964, C. V. Sridhar directed Kalai Kovil, starring S. V. Subbaiah, R. Muthuraman, Chandrakantha, Nagesh, V. Gopalakrishnan and V. S. Raghavan; Viswanathan and Ramamoorthy produced the film and composed its music.
Disagreement between the composers worsened by Server Sundaram, starring Nagesh, R. Muthuraman and K. R. Vijaya, which was released at the end of 1964.
Viswanathan and Ramamoorthy briefly reunited in 1995 for the unsuccessful Tamil film Engirundho Vandhan, starring Sathyaraj and Roja.
[9] On 27 June 2015, Viswanathan was admitted to Fortis Malar Hospital in Chennai with respiratory difficulty[10] and died there at 4:15 a.m. on 14 July.