Daventry MP Chris Heaton-Harris cut the ribbon of Harpole's post office on Friday afternoon.
The post office services have been added to Manu Singh's Harpole Village Store.
More than 50 people turned out for the event, including pupils from the village's primary school.
Mr Heaton-Harris said: "I've had a good day. It's actually really good when there's so much going on nationally, to spend time going around and seeing what's going on in the constituency, and see what matters to real people.
"I was not expecting to have 50 people turn up to a post office on a Friday afternoon."
Mr Singh and his family have run the village store for eight years.
So beloved is his store by the village residents that it beat off competition from the church, the chapel and the pubs in an informal parish poll to determine what the most popular place in Harpole was.
"It's an essential part of the community," said Harpole resident Traci Byrne. "Some people come here to have a chat and a catch-up."
"Manu is a top bloke," she added. "He goes out of his way to help people."
Customers can now use the village post office for passport and driving licence applications, as well as banking services.