The 27-year-old is returning for his second stint at Kenilworth Road after a loan spell with the Hatters from Premier League side Arsenal in January 2017, whom he joined in October 2013 after the Gunners paid £125,000 to Bristol Rovers for his services.
Macey played 13 times, keeping four clean sheets for Town, until he was recalled by Arsene Wenger to provide cover at the Emirates.
He went on to make his Arsenal debut the following campaign, starting the 2-1 Carabao Cup win over Norwich City, followed by his Europa League bow nine days later in a goalless draw against Red Star Belgrade.
The 6ft 7in stopper then joined League One Plymouth Argyle for a season-long loan in the 2018-19 season, turning out 38 times for the Pilgrims, and keeping a clean sheet when the Hatters went to Home Park that term.
Macey opted to move north of the border and sign for Hibernian in January 2021, helping his new team reach the Scottish FA Cup Final, where he saved a penalty in the 1-0 defeat against St Johnstone, plus finishing third to qualify for Europe.
Last season he made 43 appearances in all competitions and kept 14 clean sheets, but with the arrival of Scottish international David Marshall, he has opted to return to England again, joining up with the Hatters once more.