Bangladesh qualified for the tri-nations final in Ireland after another win over the West Indies on Monday.
The West Indies reached Friday's final after beating the tournament hosts Ireland on Saturday for a second time. But they lost for a second straight time to Bangladesh, when 247-9 was easily chased down by Bangladesh, which made 248-5 with 16 balls to spare.
The match was won tamely on a wide delivery by Sheldon Cottrell, but it was an all-round effort by Bangladesh.
Without haste, opener Soumya Sarkar scored 54 and Mushfiqur Rahim 63, and they were well supported by Tamim Iqbal (21), Shakib Al Hasan (29), Mohammad Mithun (43), and Mahmudullah (30 not out).
Off-spinner Ashley Nurse was the pick of the bowlers with 3-53.
Bangladesh's own bowlers set up the easy chase after restricting the West Indies to another sub-par total, AP news agency reports.
Opener Shai Hope made 87 from 108 balls and was on track to a third century in four games until he tried to pull Bangladesh captain Mashrafe Bin Mortaza and ended up being caught behind.
Hope's stand of 100 with captain Jason Holder, who racked 62 from 76, was the only partnership of substance by the West Indies. Both batsmen were out within two overs of each other.
Pacers Mashrafe and Mustafizur Rahman shared seven wickets, but the West Indies were tied down by the spinners, especially Shakib, who finished with figures of 10-1-27-1.
Bangladesh finish the round-robin against Ireland on Wednesday, preceded by the final on Friday, all on the same Malahide ground.