The 'Oh My Goodness' singer was part-way through a rendition of Stevie Wonder's 'Signed, Sealed, Delivered' when he slipped on the wet fixture and slid offstage.
Murs was unharmed after his fall and continued to sing from his landing spot out of the view of the crowd.
Taking to Twitter after the gig, the Xtra Factor host wrote: "Oooh jeez! Proper stacked it tonight on stage haha GUILFEST was sooo cool.
"Amazing you all turned up & stayed!! Specially with the rain!! X."
Murs also posted a link to the video of his fall at the Guilford festival, admitting that it "had [him] in stitches".
He added: "I'm expecting HUGE caining from this... Haha."
Cher Lloyd, Tim Minchin and Stooshe were among the other acts to play at this year's Guilfest.
Tulisa Contostavlos cancelled just half an hour before her appearance on the main stage after two days of partying in Ibiza, claiming she was "really unwell".