Mooney joins following the expiry of his contract at Altrincham where he has spent the past two seasons.
A former Wales U21 international, Mooney began his career at Fleetwood Town, joining the League One side at the age of 17. Mooney made his debut for Fleetwood in a 2–0 defeat against Rochdale in the EFL Trophy in 2018.
The 22-year-old made four appearances for Fleetwood, also spending time out on loan at Chorley and Chester, before heading to Altrincham in January 2020.
Mooney was in fine form last season, winning Altrincham’s Players' Player of the Season and the National League Young Player of the Year.
The winger also topped the Robins' goalscoring charts last season with 13 goals, while also helping out with eight assists in all competitions.
"Dan has obvious qualities," said Blues Head Coach Kevin Maher.
"A left footed player gives us balance and he's a player that will always create and score chances. I think he’s a great signing for now and for the future for us.
"It's an area we wanted to work on with goals and assists. To be a part of a team that will improve is big, he’s at a great age and what we have in the building already is important for him as he’ll only improve himself, but he’ll improve the team and others around him."
Mooney will officially become a Blues player from 1st July.