The 23-year-old arrives from Scottish Premiership side Hibernian, where he arrived in the summer for an undisclosed fee.
A graduate of the Nottingham Forest academy, Harbottle has previously played in League Two when he played for Mansfield Town last season.
He had a strong spell at the One Call Stadium, scoring six goals from defence, with the last one coming against his new club on the final day of the season. The defender also netted against AFC Wimbledon and Tranmere Rovers.
The centre-back has struggled for minutes in Scotland, only making two appearances for Hibs and only playing a total of 65 minutes in the league.
Harbottle has not picked up many minutes in his career so far, only making two senior appearances for Forest, both coming in EFL Cup matches. He also picked up National League experience with Wealdstone.
It is the third incoming transfer for the U’s this window, with Conor Wilkinson arriving from Motherwell, and Jayden Richardson coming in on loan from Aberdeen.
The Essex Club have made changes over the window, with the appointment of the Cowley Brothers to replace Matty Etherington following his sacking.
Colchester are currently 22nd place in League Two, on 25 points, six points ahead of Forest Green Rovers. The Nailsworth club have a game in hand on the U’s, who had their match against Salford City postponed last weekend.
The Cowley Brothers have their work cut out for them as they have arrived in Colchester in the midst of a relegation scrap. It could be argued that the defence is not the area the club needs to strengthen, and should focus on filling the void left by Joe Taylor’s departure to Lincoln City. Riley Harbottle is nevertheless a strong option to have in the backline.
As he proved with his loan spell with Mansfield last season, the 23-year-old can thrive in League Two and can also offer an attacking threat with his six goals for Nigel Clough’s side. Standing at 6″1, Harbottle is a strong aerial threat. The former Wealdstone defender was dominant in Nottinghamshire, and hid new bosses at the Jobserve Community Stadium will hope he can do that in Essex as well.