After returning from the Second World War, Merzhanov achieved international recognition in 1945 when he shared the first prize with Sviatoslav Richter at the Third All-Soviet-Union Piano Competition in Moscow. Viktor became a soloist in Moscow Philharmonic Orchestra in 1946. Three years later, he placed tenth at the International Chopin Piano Competition in Warsaw.
During his 60-year stage career, Merzhanov gave over 2000 recitals in Russia, Europe, the United States, China, Africa and other countries. Sergei Prokofiev chose him to give a premiere performance of the Sixth Sonata in 1948. Since the 1950s, Viktor had been performing with Avet Ter-Gabrielyan and Komitas Quartet. He appeared on stage with Lorin Maazel, Kurt Sanderling, Kiril Kondrashin, Nikolai Anosov, Alexander Gauk, Gennadi Rozhdestvensky, Yuri Temirkanov, Evgeni Svetlanov, and other prominent conductors.
In 1947, Merzhanov started teaching at the Moscow Conservatory, becoming a Professor in 1964 and Head of Special Piano Department in 2007, and also taught at the PWSM Warszawa (1973–78). His students include Vladimir Bunin, Nazzareno Carusi, Tatiana Shebanova, Anahit Nersesyan, Yuri Slesarev, Lambis Vassiliadis, Patrick Crommelynck, Ferenc Rados, Jarosław Drzewiecki, Marián Lapšanský, Frank Fernández, Allan Schiller, Galina Mieserova, Vitaly Dotsenko, Yulia Ryabova, Andrzej Kloś, Elżbieta Tarnawska, and Tatjana Ognjanovic. Viktor acted as a jury member in more than 40 international competitions, including Rachmaninov Competition (which he founded), International Tchaikovsky Competition in Moscow, Chopin Competition in Warsaw, Bartók-Liszt Competition in Budapest, and other contests in Montreal, Tokyo, and Brussels.