The 28-year-old left-back, who spent three seasons playing for Aberdeen in the SPL, has joined the Quakers until the end of the season.
He becomes Darlington's eighth signing during January.
Byrne, who has been given squad number 33, spent the second half of last season with Inverness Caledonian Thistle after joining them from Oldham Athletic last January, and also had a loan spell
with St Johnston earlier this season.
The Dubliner played 59 games for Aberdeen from 2005-08 after two seasons with Dunfermline, who’d signed him from Shamrock Rovers in 2003. He helped Dunfermline reach the 2004 Scottish Cup Final.
Byrne joined Shamrock in 2000 and was their Young Player of the Year in his first season, and went on to make six appearances in European competition for the Hoops, two in the UEFA Cup and four in
the Intertoto Cup.
Meanwhile, young midfielder Dan Riley has joined Northern League first division side Billingham Town on loan for a month.