The rapper topped the poll with 19.3% of the vote with his iLL Manors album, picking up 490 of the 2,560 votes cast.
Meanwhile, Jessie Ware's Devotion finished a close second at 18%, followed by Ben Howard's Every Kingdom with 17.3%.
Bookies' favourite Alt-J picked up a 15% share for An Awesome Wave, while Roller Trio's Trio and Sam Lee's Ground of Its Own came joint-last with just 0.5% of the vote each.
It was recently reported that all 12 nominated acts have seen a significant sales boost since the nominations were announced in September.
This year's Barclaycard Mercury Prize will be announced at London's Roundhouse.
The Digital Spy poll results appear in full below:
Alt-J: 'An Awesome Wave' - 15.0%
Django Django: 'Django Django' - 4.7%
Field Music: 'Plum' - 1.6%
Richard Hawley: 'Standing at the Sky's Edge' - 4.0%
Ben Howard: 'Every Kingdom' - 17.3%
Michael Kiwanuka: 'Home Again' - 3.6%
Lianne La Havas: 'Is Your Love Big Enough' - 7.0%
The Maccabees: 'Given to the Wild' - 8.5%
Roller Trio: Roller 'Trio' - 0.5%
Sam Lee: 'Ground of Its Own' - 0.5%
Plan B: 'Ill Manors' - 19.3%
Jessie Ware: 'Devotion' - 18.0%
Watch the music video for Plan B's new single 'Playing With Fire' below: