Stepan Demirchyan was born in Yerevan and received his degree from Yerevan Polytechnic Institute in 1981. He is an engineer-electrician and a PhD on Technical Sciences. From 1981 to 1986 he worked first as a skilled worker and later senior skilled worker, supervisor-probationer, head of station and then deputy head of the assembly shop in the Electrical Engines Industrial Complex under the Ministry of Electrical Technologies Industry. From 1984 to 1986 he worked as an assistant engineer in the Electrical Engines Industrial Complex. From 1986 to 1988 he worked first as a chief engineer and later as acting director in the Construction Plant of Programming Equipment under the USSR Ministry of Equipment, Automation Means and Management Systems. The next fifteen years were spent as the general director of the Mars Industrial Complex.
He was a candidate in Armenia's 2003 presidential election.
Demirchyan is married and has three children.