The Burberry designer is tying the knot with the actor at the end of September in an intimate civil ceremony in front of close family and friends, according to The Daily Mail newspaper.
The happy couple - who first met in 2009 - were seen at a Chelsea Register Office in London earlier this week to arrange their union and it is thought they will be inviting only a handful of guests to the venue.
They were first introduced by Chelsea Clinton and her husband Marc Mezvinsky at their wedding, where Christopher designed the suits for the groom and ushers.
The 40-year-old creative director - who has been awarded an MBE for his work in fashion as well as several Designer of the Year awards - previously suffered heartache when his boyfriend, Miu Miu's director Geert Cloet, tragically died of brain cancer in 2005.
The designer has a busy month ahead, planning his show for London Fashion Week and putting the finishing touches to Burberry's Spring/Summer 2013 collection.