Former Forest Green midfielder has joined League One rivals Exeter City on a two-year deal.
The former Celtic academy graduate spent more than two years at Barnsley and also had loans at Stevenage and Forest Green, winning the League Two title under Rob Edwards and scoring six goals in 30 appearances.
Aitchison told Exeter City’s website: “It’s all happened very quickly, but as soon as I spoke to the manager I knew I wanted to sign. It’s a club that already feels a little like home – I know James [Scott] from youth level, and Kyle [Taylor] from Forest Green so I feel at home straight away.
“When I spoke with the manager, I knew straight away I’d fit into this team.”