The 27-year-old, whose switch to stadiummk will be completed once the transfer window opens, has played just three times for Albion this season.
Harley, who began his career with Bristol City, netted over 30 goals in almost 150 games for Exeter during a three-year stay in Devon. He moved to Swansea but never made an appearance before signing for Gus Poyet's men.
The playmaker has made a total of 18 appearances for the Seagulls, scoring twice, and is set to be involved in the Dons' npower League One match against Notts County.
