The duo was performing together in the UK live for the first time at the festival, reported Entertainment Weekly.
"Get Lit" is their first song together since 1998's "Lovely Daze" on the DJ Jazzy Jeff & The Fresh Prince Greatest Hits record.
Addressing the crowd at Blackpool's Tower Headland Arena, Smith confessed that the pair had been preparing a new record "that you haven't heard yet." He went on to explain that "Get Lit" was a track made in response to the recent "chaos and confusion" in the world.