Besides a solo career, he was the member of bands Bergendy and V'Moto-Rock, and played an important part in the rock culture of the country, contributing to nearly 150 albums.

His father was an engineer at the Diósgyőr Steel Company, and after he was fired because of political reasons, the family moved to Budapest, where he got a ministry job.

Demjén, who graduated as a chemist technician, was inspired by his fathers singing talent, and started to study music, largely on his own.

He debuted as a songwriter with Jöjj vissza vándor, scoring his first success, resulting in weekly performances in the popular E-Klub and Ifjúsági Park.

After V'Moto-Rock disbanded in 1988, Demjén began a solo career, releasing an album almost every year in the nineties.