Batting first, Hayleys posted 127 runs in 19.3 overs, with key contributions from Sadeera Samarawickrama (33), Nishan Madushka (27) and Ramesh Mendis (29).
In reply, CDB was bowled out for 122 in 19.5 overs, with Hayleys producing a disciplined bowling display.
Ramesh Mendis led the attack with 3 for 21, supported by Ravindu Fernando (3/24), while Prabath Jayasuriya, Kavishka Anjula, and Kalana Perera picked up a wicket each.
Mendis was named Player of the Final for his all-round performance.
With this win, Hayleys has now reached the finals of all three Mercantile Cricket tournaments this season, securing two titles.