The couple, understood to both be in their 80s, were discovered in the property in Upper Ramone Park in the Portadown area by a relative.
It is thought the man and woman were stabbed by an intruder to their home.
A man, aged 40, was arrested by policing investigating the murder and is being questioned by detectives in custody.
At a press conference in Portadown late tonight Detective Superintendent Kevin Geddes described the double murder as a “very brutal attack”.
He did not name the victims and said it was too early to comment on many aspects of the case.
It emerged that a grey Renault Kangoo van was stolen by someone who police believe was in the couple’s house at around the time of the murder – 12.30pm yesterday.
It was around three hours later they were discovered by a relative.
Police and forensic officers were at the scene in the quiet residential street near Craigavon Area Hospital at around 4pm yesterday.
Mr Geddes appealed for anyone who observed the movements of the van to come foward as they believe the theft of the van may be linked to the murder.
The van was recovered in Edenderry, a short distance from the couple’s home.
The suspect was arrested in Springfield housing development – also close to the scene.
Ulster Unionist Doug Beattie MC said: “This is a very quiet area of Portadown which has been visited by an absolutely terrifying situation this afternoon.
“An elderly couple in their 80s have been murdered in their own home and my thoughts and prayers are with them, their family and their friends.”