The 'Shame' star and the Mumford & Sons musician have both spent large parts of the last year away from their home country due to work commitments, but are looking forward to coming back to the UK for their big day.
A source told The Sun newspaper: "Both Carey and Marcus have been so busy recently.
"She's been filming 'The Great Gatsby' in Australia and he has locked himself away in the studio with the rest of Mumford & Sons to record their new album. ------------------- Read more: More celebrity news from IrishCentral
"They've finally got around to choosing a date and place for the wedding and sent out all of the 'save the date' cards to guests. They decided it makes sense to have the nuptials in Britain because it's where both of their families are from."
The couple met in February 2011 after she attended one of his concerts in the US and they were engaged in August of that year.
The pair had, however, known of each other for some time, as they were pen-pals as children, but had not been in touch with each other for years.