Britain and Canada will establish joint diplomatic missions and share embassy offices abroad, Foreign Secretary William Hague is set to announce.
Mr Hague will reveal more details of the plans when he meets his Canadian counterpart, John Baird, in Ottawa later, a Foreign Office spokesman said.
The proposals involve "co-locating" embassies and sharing consular services in countries where one of the nations does not have an embassy, the spokesman said.
Mr Hague and Mr Baird will sign an agreement and hold a press conference later on Monday to explain more about the plans.
Ahead of the meeting, Mr Hague said: "As the Prime Minister said when addressing the Canadian parliament last year: 'We are two nations, but under one Queen and united by one set of values'.
"We have stood shoulder to shoulder from the great wars of the last century to fighting terrorists in Afghanistan and supporting Arab Spring Nations like Libya and Syria. We are first cousins.
"So it is natural that we look to link up our embassies with Canada's in places where that suits both countries. It will give us a bigger reach abroad for our businesses and people for less cost."