The 27-year-old became the Shrimps’ fourth summer signing after agreeing an initial one-year deal at the Globe Arena.
He made the move following a two-and-a-half-year spell with Tranmere Rovers, for whom he appeared as a substitute in their play-off final win against Newport County AFC last season.
He told the club website: “I’m looking forward to getting going. I know a lot of the lads already and played with Cole Stockton and Ritchie Sutton at Tranmere recently too so that will be good.
“I’ve had a couple of good years with Tranmere with three play-off finals and two back-to-back promotions and it will be great to try and carry on that success this year.
“I was meant to sign for Morecambe on loan from Wigan a few years ago but the club was under an embargo then and I went to Burton instead so it’s good to finally get here.”
Buxton began his career as a youngster with Wigan Athletic, where he was loaned out to Burton Albion and Accrington Stanley before joining the latter permanently in 2014.
Two years with Stanley ended when he declined a contract extension in favour of what proved to be a short spell with Portsmouth.
He only made four appearances before his contract was cancelled by mutual agreement in January 2017, allowing him to join Tranmere the following month.
His arrival fills the gap created by Zak Mills’ departure after he turned down a new contract and opted to join Oldham Athletic.
Bentley said: “We’ve nearly signed Adam a couple of times since I have been manager.
“After Zak Mills’ departure it was important that we got quality into the squad and I feel we’ve done that.
“His main position is right-back but he can cover anywhere in defence.
“He’s well respected by staff, fans and team-mates at Tranmere and played a big part in their promotions.
“He’s experienced at the level, he’s a good footballer, a solid defender and we wish him well for the season ahead.”