The actor, who played Neville Longbottom in the hit film series, is set to marry girlfriend Angela Jones, after reportedly popping the question in front of the Eiffel Tower in Paris in November.
'They're both over the moon. They got together in July and hit it off straight away,' a representative for the couple said in a statement.
Matthew and Angela met in January, when he attended an event at the Wizarding World of Harry Potter at Universal Studios in Orlando, where Angela works.
Matthew and Angela dining with a friend in London
The 27-year-old looks set to become the first of his Harry Potter co-stars to tie the knot. Bonnie Wright, who played Ginny Weasley, got engaged to Twilight's Jamie Campbell Bower in 2011, but the pair called off their relationship the following year.
Matthew has gone on to have many notable career successes since the franchise ended in 2011, appearing in films including Me Before You and TV shows such as Ripper Street and Happy Valley.
Tonight I found myself eating a sausage out of a napkin in Al Murray's kitchen. That's showbiz. pic.twitter.com/UUiaUSX4fP— Matthew Lewis (@Mattdavelewis) December 20, 2015
The couple pose for a picture with a friend
However, he remains a huge fan and advocate of other Harry Potter projects, including the stage play The Cursed Child, which he wrote about recently on his Instagram account.
''A giant congratulations and an even bigger thank you to these guys and the rest of the cast of #CursedChild,' he said.
'To be in the movies was a dream come true but it became work and I forgot what it was to be a fan a long time ago.'
'However, over the last two nights I was able to enjoy the world of 'Harry Potter' once again. To lose myself in a story so rich and so powerful and, more importantly, that I had nothing to do with was truly magical.'