The creative player will officially link up with the Pilgrims on July 1 following the expiry of his contract at National League rivals Altrincham.
Mooney holds the distinction of scoring the last-ever goal at York Street - with Altrincham winning the National League North promotion final, behind-closed-doors, in August 2020.
The 24-year-old has since split his playing time between Altrincham and Southend United - having previously turned out for Fleetwood Town and Chester FC.
Mooney becomes the third arrival of the summer - following in the footsteps of midfielder Frankie Maguire and defender Kieran Coates.