The 6ft 7in shot-stopper has agreed a deal until the end of the 2020/21 campaign and will provide competition for Kevin Dabrowski and Ofir Marciano.
Macey, 26, played just two competitive games for the Gunners but spent time on loan at Accrington Stanley, Luton Town, and Plymouth Argyle.
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Hide AdJack Ross admitted earlier this week that he was keen to sign another goalkeeper after recalling Dabrowski from his loan at Dumbarton.
Back-up ‘keeper Dillon Barnes was recalled by parent club QPR earlier this month and injury to Marciano had left the Capital club with goalkeeping coach Craig Samson as the only fit senior goalie at the club.
Ross said: “We are delighted to be able to bring a goalkeeper of Matt’s calibre to the club and I’m looking forward to seeing him challenge Ofir and Kevin for a place in the team.
“It provides us with real strength in depth in the goalkeeping department as we build towards the second half of the season.”
Macey added: “I’m really excited to get going. I spoke to the gaffer and Craig Samson but, to be honest, my mind was already made up to come.
“I’m grateful for every experience I had at Arsenal but I’m hungry to play first-team football. I know that won’t be handed to me here, so it’s up to me to show what I can do in training and take it from there.
“No-one has to tell me what a big club Hibernian is, in a competitive league. I’m looking forward to getting started.”