Dappy, who found fame in the band N-Dubz, was said to have held his head in his hands as the verdict was read out at Chelmsford Magistrates Court.
The singer, real name Dino Costas Contostavlos, slapped clubber George Chittock in the smoking area of Chicago's nightclub on 27 February following a personal appearance.
Taking to the stand yesterday (18 June), 27-year-old Dappy had told the court that he lashed out in "self-defence", saying he was worried the victim was going to "stab" him.
"I was scared someone was going to put a hole in me," Dappy said. "I have had to deal all my life with people trying to cut me and taking cheap shots. I don't want to get stabbed. I don't want to get hurt again."
He had denied the charge at an earlier hearing, however, magistrates today returned a guilty verdict after dismissing his version of events.
Dappy was handed an £800 fine and ordered to pay an £80 victim surcharge and £930 costs. His former CBB co-star Jim Davidson had previously sat in court to support his friend.