He was born in Yerevan. He was also known by the name "Lalik". At the age of 5–6 he sang folk songs, and later played the clarinet. Sergey Karapetyan began his musical career in the folk instruments ensemble led by Artem Mejinyan, and his first working steps were in Vardan Buniatyan's group. In 1952 he worked for one year in Gurgen Mirzoyan's group. In 1964 Karapetyan joined the Folk Instruments Ensemble of Armenian Television and Radio. From 1978 he became a soloist. In 1978–88 he worked at the Sayat-Nova Music School in Yerevan, where he was the first teacher of the duduk-shvi department. He toured in many countries of the world. In 1989 he was awarded the title of Honored Artist of Armenia, and in 2008 the "Movses Khorenatsi" Medal of the Republic of Armenia. He died in Yerevan.