The couple, who have been named locally as Donald and Maureen Macmillan, were discovered outside the house in Gravir in the South Lochs area overnight.
They ran the post office in the small community about 25 miles south of Stornoway.
Mr Macmillan was in his 70s and had been with the post office for almost 50 years.
It is not clear yet how or why the couple ended up outside as temperatures dipped below freezing.
People in the community have been shocked by the news, saying the Macmillans were well known in the community and a lovely couple.
Police Scotland said officers were at the scene and their investigation was at “a very early stage”.
The deaths are currently being treated as “unexplained”.
Murdo MacLennan, a local Free Church elder, has paid tribute to the couple, describing them as “lovely”.
He said they would be missed in the local community.