The move is subject to international clearance, which if it comes through, will see Hyndman become available for Hibs' Europa League clash against Molde on Thursday night.
The American said: "I am delighted to have joined Hibs. I enjoyed my previous time in Scotland - my game is well suited to the style of play here.
"I'm looking forward to meeting up with the squad and hopefully working my way into the team."
Hibs head coach Neil Lennon added: "We are pleased to bring in a player of Emerson's quality.
"Technically he's at a good level, he's got experience of the Scottish game and gives us another option in the centre of midfield."
Hyndman spent time loan with Rangers in 2017.