Speaking ahead of the show's premiere on March 24, the hip hop star said that despite previous reports, she would be critical of the singers.
Jessie, who is one of four music coaches on the new BBC One series, insisted: "I'm not scared of being critical"
And she promised that the feedback wouldn't be all "You go, girl" platitudes.
The 'Domino' hitmaker is joined by Will.i.am, Tom Jones and Danny O'Onoghue on the panel, who are looking set to go head to with Britain's Got Talent on Saturday nights.
Hosted by This Morning star Holly Willoughby and Radio 1 DJ Reggie Yates, the series has teamed up with Universal Music to give the show's winner a recording contract.
The programme will also feature guest performances, with the Independent reporting that the likes of Robbie Williams, Sir Paul McCartney and Madonna could all appear on the show.
The Voice UK starts on March 24 on BBC One.