The royal, who is often seen at rugby and polo matches and recently hosted a Christmas Eve football match for staff at Sandringham, dressed casually in a white T-shirt, grey cardigan and trousers for the sporty event.
He was seen laughing with his friends as he watched Stephen Bunting beat James Wade 4-1.
Harry wasn’t the only famous face at the event – TV presenter Clare Balding and football referee Howard Webb were also among the crowd.
The popular royal's appearance went down well with one of the evening's champions, Stephen, otherwise known as "The Bullet", who later joked: "I didn't know Harry was here. I'm going to have a pint with him now! But it is great that darts is getting this type of coverage."
Harry recently used his position and love of sport to encourage more schools across the United Kingdom to play rugby.
The young prince and trained rugby coach took part in a training session involving youngsters who play the sport in Salford, Manchester.
Wearing an England rugby shirt, the 30-year-old was enthusiastic as he joined in with the practise session at Eccles RFC.
During his visit Harry also helped student volunteers run a rugby festival for younger children, and he met with local teachers who are being trained as rugby coaches.