The 19-year-old has departed the U’s after six months at the JobServe Community Stadium, having signed for them on a short-term contract from Nottingham Forest at the end of the summer transfer window.
Thompson arrived at Colchester as part of the loan agreement that saw them sign fellow Forest youngsters Aaron Donnelly and Jamie McDonnell on loan from the Premier League club.
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He has now returned to Northern Ireland and boss Colchester boss Danny Cowley believes it will be a good move for the versatile youngster.
Cowley said: “He came over from Northern Ireland to Nottingham Forest with real potential but has had some really bad injuries, leg breaks and things haven’t gone for him, from an injury perspective.
“But there’s a good player in there and he’s someone who just needs first-team football now and we wish him well.”
Harps boss Darren Murphy told the club’s media: “I’m absolutely delighted to welcome Joel to the club.
“He’s a superb talent who has been unfortunate with injuries since making the move across the water and so it’s brilliant to have him here at Finn Park.
“He’s eager to prove himself in senior football and he gives us options in a couple of areas of the pitch.
“He has fit in seamlessly to the group and I’m excited to work with him for the season ahead.”
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Thompson joined Forest when he was 16 after impressing for Northern Irish side Crusaders and spent two years at the City Ground club.
The Northern Ireland under-19 international joined Forest in July 2022, who is comfortable playing left-back and centre midfield, and departed the City Ground after two years to join Colchester United.
