Crowned champion jockey on the Flat in Ireland at the end of last year, the 19-year-old successfully applied to the Irish Turf Club for a jumps licence to allow him to ride at the Festival.
O’Brien, who won the 2000 Guineas and the English and Irish Derbies on Camelot last year, takes the mount on Shield, trained by his father Aidan.
While the young jockey has yet to experience the Mecca of jumps racing, his father is no stranger to the meeting. His winners include the triple Champion Hurdle winner Istabraq.
O’Brien jnr is hoping for beginners’ luck when he gets the leg up on Shield, who got off the mark at Leopardstown just a fortnight after finishing fourth on his debut at Punchestown.
Those performances were just enough to book him a place in the field.
“Obviously he just got in the race at the bottom,” he said.
“First time out he got tired in very bad ground at Punchestown and we had to run him quite quick to qualify for the race in case he ended up going there.
“He won nicely in Leopardstown and hopefully he will have come on for the run.
“I’ve never actually been to Cheltenham before. It can be a rough race, but I’m looking forward to something different.”
Another Flat champion looking to turn over the jumps boys is Britain’s number one, Richard Hughes.
He has ridden at the Festival several times before without success and is hoping to break his duck on two-time winner Sgt Reckless for Mick Channon.
“I hope I’ve got a good chance. I rode him work and I liked him. He certainly goes there with a chance.
“It’s a rough race and you need luck in running.”
Tony McCoy, Britain’s 17-times jumps champion, won this race on Liberman in 2003 and this time has the mount on Regal Encore for his boss JP McManus and trainer Anthony Honeyball.
“The horse is fine and we’re ready to go,” Honeyball told At the Races.
“I’m really excited. He’ll be judged on what he does at Cheltenham and however he runs, we know we’ve got a nice horse.
“We think he’s got what it needs to be there or thereabouts. We’re looking forward to it.”
Champion Irish jumps trainer Willie Mullins has his usual strong team as he goes for a remarkable eighth triumph in the Bumper.
“Briar Hill doesn’t show me much at home, but he appears to save his best for the track,” he said.
“Sizing Tennessee and Union Dues have both won their last two and are in good form, so we’ll see what happens.
“They all have form in soft ground.”
Andrew Lynch, who rides Sizing Tennessee, said: “He’s won two bumpers and he goes well. He’s a nice horse, but every horse in the race is fancied.
“This is my first ride in it and I’m looking forward to it.”
Nigel Twiston-Davies is hoping there is a good gallop for his runner Pure Science.
“I hope he has a bit of a chance, as long as it’s a truly run race,” said the Naunton trainer.
“The pace was too slow for him last time (fourth at Newbury) and I think he will show he’s better than that. He’s in good form.”