Police and paramedics were called to a property in Station Road in Shirebrook, near Mansfield, shortly after 10pm yesterday.
The two bodies were found inside, Derbyshire Constabulary said.
A force spokesman said: “An investigation has been launched into the circumstances surrounding the discovery, but the deaths are being treated as suspicious.
“A 20-year-old man was arrested earlier today and remains in police custody.”
A man who works at a nearby business said police and forensics officers were “everywhere” on Station Road, near the junction of Hardwick Street.
Part of the street around the Road and Rally Discount Accessories motor spares shop was cordoned off as officers investigated the deaths.
The man, who asked not to be named, said police activity appeared to be centred around a terraced house in the east of the mining village, not far from the railway station.
He said: “There are police and forensics teams everywhere and it is all cordoned off.
“The front and back of a house are cordoned off and there is a police car down at the bottom at the back.
“There are lots of forensics vans and they’ve also cordoned off the houses next door.”
Another business owner said the incident had occurred seven or eight houses down from the junction with Hardwick Street and that the property had been surrounded by police all morning.
The man described the area as quiet and residential, saying: “I have worked here 10 years. You get a bit of trouble here but you get that anywhere – but nothing major at all. This is a bit out of the ordinary.
“The police have not been in here and told me anything.”
Anyone with information about the incident is asked to contact Derbyshire police.