"Variant of Melanie"
The name Mellie is commonly a female name from the "Greek" origin.
Mellie is an English familiar form made with the -ie diminutive suffix, attached to names containing the element mel-, among them Melanie, Melinda, Melissa, Amelia and Millicent. It has no root or meaning of its own; the sense comes from whichever fuller name it shortens. The spelling in -ie rather than -y is one of the standard spellings recorded for English diminutives of this type.
Melanie means "Dark-haired".
The pronunciation of Mellie is MEL-ee.