The former Chelsea ace saw his short-term contract at Stadium MK expire at the end of June, but he has finalised tersm on a new deal to continue his career with the Dons.
McEachran initially moved to MK in January, and made 14 appearances as Russell Martin s team finished the season 13th place in Sky Bet League One.
The 28-year-old has endured a testing summer, which including contracting Covid-19, and that means he has only recently began his pre-season preparations.
But McEachran is confident he will soon catch up with his Dons team-mates and be ready to resume his MK career.
“I’m really excited to be back,” said McEachrean. “It’s been a long few weeks, getting things sorted, but I’m delighted to be here again and I’m excited for season ahead.
“This was a perfect fit for me last season and I was able to come in, get 14 games under my belt and help the team finish the season strong. I absolutely loved my time here so it was a no brainer to come back here.
“Unfortunately, I suffered with Covid this summer which has meant I’ve only just been able to start my pre-season training.
"It will take me some time to get up to speed but, week by week, I’m feeling fitter and stronger – hopefully it won’t be too long before I’m back on the pitch.”
Oxford-born McEachran began his career at Stamford Bridge and made 22 senior appearances for the Blues, while also having loan stints at Swansea City, Middlesbrough, Watford, Wigan Athletic and Vitesse Arnhem.
In the summer of 2015 McEachran joined Brentford for a £750,000 and went on to play more than 100 games for Bees, before making the switch to Birmingham City.
He only made 10 appearances in 18 months at St Andrews, before making the switch to Dons in January.
MK boss Russell Martin said: “We’re really pleased to be able to keep Josh at the club.
"We all know how good he is from what he was able to do last year – he is a fantastic footballer who was getting better and better every week.
“We will have to get him back into a top physical condition over the next few weeks before he’ll be able to add to us on the pitch.
"Once he’s back, I’ve no doubt that he’ll give us that control and confidence in the middle of the pitch.”