O’Brien, twice champion Flat jockey in Ireland, has quit the saddle to concentrate on his new role.
The 22-year-old has been playing a key role in helping his father, trainer Aidan O’Brien, with a large string of horses recently, including JCB Triumph Hurdle favourite Ivanovich Gorbatov, from a base at Piltown, County Kilkenny, where the great Istabraq’s triumphs were originally masterminded.
He said: “My grandad trained from here and both my mum and dad trained from here. The last couple of years we’d had horses back here and it’s gone on from there.
“I’ll just take things as they come and do my best with every horse that comes in and go from there. I’ll just do my best with all the horses and see what happens after that.
“Hopefully I’ll have the licence for May. That’s the plan at the moment.
“We’re pretty much 50-50 jumpers and Flat horses. We’ve got a nice bunch of two-year-olds and some National Hunt horses.
“Hopefully we can get a few winners when the season gets going.”
Tall for a Flat jockey, O’Brien was always likely to find his battle with the scales proving too much.
“Starting off, I never thought I would be able to ride for an awful long time,” he said.
“I was very lucky to ride some very good horses. I was in the right place at the right time.”
Of his many big-race triumphs, O’Brien rates the Epsom Derby, which he won twice on Camelot (2012) and Australia (2014), and the Breeders’ Cup Turf on St Nicholas Abbey in 2011 as career highlights.
He said: “I just started off wanting to ride a few winners and things kind of went from there. You don’t ride big winners if you don’t ride good horses, so I was very lucky.
“Riding the winner of the Derby is something else. It’s the history the race has and everything about it — the day and the build-up to it. It’s very hard to equal the Derby.
“The Breeders’ Cup is a huge stage and to ride there was unbelievable and to win there was something you wouldn’t even dream about happening.
“I would have carried on riding over jumps but things on this side have happened a little bit quicker than maybe what I was expecting and it’s very hard to do one thing right, let alone try to do two things. It makes a lot more sense to concentrate on one thing.
“Training horses is different to riding, but it’s the same kind of kick when things come right. There’s a lot more goes into it.”
Mick Kinane expects O’Brien to make a seamless transition from top jockey to successful trainer.
Kinane was one of Ireland’s best-ever Flat jockeys, winning the title 13 times in a 34-year career that ended in 2009.
He was stable jockey at Ballydoyle between 1999 and 2003 in which he rode such stars as Galileo, Giant’s Causeway and Rock Of Gibraltar. In 2001 alone they teamed up to win 17 races at Group One or Grade One level.
O’Brien was also number one at Ballydoyle and Kinane believes the 22-year-old did “remarkably well” in a difficult job especially when at such a tender age.
“For one so young he achieved an awful lot as a jockey. He can be proud of what he achieved,” said Kinane.
“It’s all about success at Ballydoyle and they need stallions every year. He handled the pressure that goes with the job remarkably well.
“It’s a very powerful stable but he had to get the job done.
“He should get the right support and he’s training from a nice establishment. I’d expect him to be a success.”
Meanwhile, The Grey Gatsby has been earmarked to begin his season at the Curragh in May after trainer Kevin Ryan resisted the urge to send him back to Dubai.
Ryan had considered a return to Meydan, this time for the mile-and-a-half Sheema Classic, for the consistent five-year-old after he chased home Solow in the Dubai Turf 12 months ago.
The son of Mastercraftsman will instead be kept under wraps for a few more months, with the Tattersalls Gold Cup at the Curragh — a race in which he was fourth last year — a possible first objective.
The Grey Gatsby is then likely to head to Royal Ascot for a repeat bid in the Prince of Wales’s Stakes after he finished a short-head second to Free Eagle last summer.
Ryan said: “We’ve decided that it (Dubai) would come too early in the year for him.
“He’s in great form — he’s wintered really well — but we’ll probably start him off at the Curragh before Ascot.
“If we start later with him, hopefully we’ll be able to keep him going for longer.”