The 26-year-old will remain at Pittodrie for the rest of the current campaign, but has signed a pre-contract agreement that will see him move to Stadium MK on a two-year deal this summer.
The move brings an end to a 10-year stay at Aberdeen for the former Scotland Under-21 international, during which time he made more than 200 appearances for the club.
"I'm delighted to sign for MK Dons. I think it's the right time in my career to come down to England. As soon as I heard of the interest, I knew that this was where I wanted to be – this is a great club with a great stadium and it was a huge attraction for me," he told the club's official website.
"The ambition and potential here is huge so hopefully I can come here next season and we can really progress – I'm really looking forward to it."
Manager Robbie Neilson added: "I'm looking forward to getting him down here next season. He's had a really good career in Scotland and played a lot of games at a real high level.
"He feels it's time for him to make that next step and hopefully we can provide the platform for him to do that. He's direct, quick and makes things happen – he's the type of player I think we need at this club. Hopefully he can come down and replicate the good performances he's had up at Aberdeen."
Pawlett has made 18 appearances in all competitions for Aberdeen this season, but has only been named in the starting lineup on seven occasions.