Trump let slip a 5-1 lead and his opponent had chances to force a decider, but eventually the young Bristolian knocked in excellent pots on brown and blue in the tenth frame to seal the victory.
In a meeting between arguably the two most exciting talents in the sport, he will face O'Sullivan over 19 frames on Sunday (1pm and 7pm) for the title and £150,000 top prize. It will be a repeat of last month's Champion of Champions final, when O'Sullivan won 10-7 in one of the highest quality matches of recent years.
Trump will be aiming for his fifth ranking title and second of the season, having won the Australian Goldfields Open. The 25-year-old left-hander will also be targeting his second UK Championship crown having triumphed here in York in 2011 by beating Mark Allen in the final.
Some tremendous potting - and breaks of 57, 63 and 79 - helped Trump to a 4-0 lead. Glasgow's Maguire pulled one back then a run of 100 from Trump made it 5-1. Maguire, who won this event ten years ago, made a 67 to take frame seven added the next for 5-3. Trump had a clear chance to seal victory in the next but lost position in potting the green and missed a cut-back brown. Maguire gratefully cleared for 5-4.
Frame ten also came down to the colours and Maguire went in-off escaping from a snooker. Trump slotted in the green then potted a superb brown to a blind baulk corner. He added the blue to middle to go 16 points ahead, and rolled the pink over a pocket to invite the handshake.
"I had chances to finish it and once it went to 5-3 the pressure was on me, especially with Ronnie waiting in the final of our second biggest event," said Trump. "I'm more consistent than ever and this is my third final of the season. I'm excited about tomorrow.
"Ronnie will raise his game and he is massive favourite. In the Champions of Champions final he played perfect snooker and he might not be that good again, so I need to take my chances. People have been twitching against him this week because it's Ronnie. I always enjoy playing him - who wouldn't relish the chance to take on the best player ever?"
Maguire said: "I can't complain because I had chances to go 5-5. Early on he potted some great balls and played well to be 5-1 up. Once I had got back to 5-4 I honestly thought I would win. When he missed the chance to win 6-3 I thought he'd had it. It's a sickener because I could have won the next frame as well."
