Danyelyan was born on July 31 1929 in Baku. He made his debut in 1956 at the Opera and Ballet Theater in Azerbaijan.
In 1957, he graduated from the Baku Music School A. A. Milovanova and that year, he became soloist at the Opera and Ballet Theater
His Repertory included German, Manrico, Radames, Otello, Don Carlo, Riccardo, Canio, Cavaradossi, Don Josť,
Tannhäuser, Oedipus Rex, Ovol (Ovol by Spadavekkia), Alexey (Optimisticheskaya Tragediya by Kholminov),
Mindia (Mindia by Taktakishvili), Abovyan (Abovyan by Armenyan), ..
Since 1968, he taught singing at the Yerevan State Conservatory (since 1976 as Associate Professor).
His students included the tenors Araik Avanyan and Gegham Grigorian.
According to Ashok Arakelyan, Sergey Danielyan never made studio recordings, however he did sing on TV.