The former Oasis star - who raises sons Donovan, three, and six-month-old Sonny, with his fiancee, and has an 11-year-old daughter Anais with his ex-wife Meg Mathews - proposed to Sara in October and now plans to make their 10-year relationship official because he thought it was the right time to do the "romantic thing".
A source told The Sun newspaper: "Noel secretly asked Sara to marry him on her birthday last October.
"He`s not one for making a big scene. This is the man who kept his leather jacket on when his lad Donovan was born. They have been living like they were married for years anyway, but now they have a family together Noel thought it was the right time to do the romantic thing.
"He splashed out on a mega posh Solange Azagury-Partridge ring from a Bond Street (London) jewellers. They are madly in love and spend all their time together without any bickering. They are a perfect match."
Among the celebrities they are planning on inviting to the event are A-list friends Russell Brand and his spouse Katy Perry.
However, his brother and former Oasis bandmate Liam Gallagher - who now fronts new band Beady Eye - is unlikely to be invited to the impending nuptials as he and Noel haven`t spoken since the band imploded in August 2009.
When Liam married his partner Nicole Appleton in February 2008, the singer didn`t even tell his sibling he was tying the knot, leaving Noel to stay in the US working on the band`s final studio album `Dig Out Your Soul`.