Wearing the purple and white of Derrick Smith, also part-owned by Sue Magnier and Michael Tabor, and trained by the jockey's father, Aidan, Leading Light could be another star for the Coolmore and Ballydoyle team.
The 7-2 favourite gave O'Brien junior his first Leger and the trainer his fourth as well as completing a full set of Classics in Britain and Ireland for Smith. He proved well up to the task on Town Moor and put himself in line to be supplemented for the Qatar Prix de l'Arc de Triomphe.
Ridden positively, the Queen's Vase winner finished a length-and-a-quarter clear of Oaks heroine Talent with twice Derby-placed Galileo Rock three-quarters of a length away in third.
The winning jockey said: "I was going to take my time but there wasn't much pace early on, so I gave him a little nudge to get him up there.
"He was very relaxed and I got him where I wanted. He won a Group Three over a mile-and-a-quarter on good to firm ground at the Curragh in May so he's very versatile trip-wise.
"I suppose this makes it a little bit sweeter after last year, but there's nothing I can do about that now and you have to look forward.
"I don't see why he shouldn't go for the Arc. He races quite lazily and even though he's won over a mile and six and over two in Ascot, he doesn't need to go that far. I'd have no trouble dropping him back to a mile-and-a-half.
"It's great to wear the cap for winning the Leger. I hope I can win another one."
His father said: "This horse stays and he quickens. He's a very solid horse, his form going into Ascot was mile-and-a-quarter form. The lads wanted him to go for that race [the Queen's Vase], but he has plenty of class.
"He's versatile trip-wise, it was a big jump up to two miles at Ascot, he's a good horse. The lads will make the decision, but the Arc would be open to them if they wanted to do that. We'll see, they'll probably talk about it next week.
"I keep saying it, but it's a privilege for us to be involved with the team. We really appreciate it, to have good horses to ride and train. It's a big team effort and we're a very small part of it."
Coolmore supremo John Magnier said: "We will look at the Arc now, he's got plenty of speed. We will talk about that.
"The ground in Paris is soft at the moment. We were going to run Camelot [in a trial at Longchamp on Sunday] so that would be doubtful and it would open it up for Leading Light, but he would have to be supplemented.
"We've always liked this horse and thought he was a good thing at Ascot [in the Queen's Vase].
"He was going to have a prep over here, but that didn't happen so that was the worry, he should improve for the run."
Ralph Beckett was delighted to see Talent bounce back to form after a below-par effort in the Irish Oaks.
He said: "The winner won well, but Talent has run well. I'm thrilled to bits with her and I feel like I have won as her last run was so bad in Ireland, for her to come back and do that it's terrific.
"All being well, if the ground comes up similar to today, we'll run in the fillies' race at Ascot on Champions Day."
Magnier's son-in-law David Wachman said of Galileo Rock: "He's a wonderful horse, he ran a blinder, but the Oaks winner just came and did us for second. The winner won very well. I suppose at least the right team won if we weren't going to.
"We'll see how he comes out of the race, but he's had a light enough campaign. I might travel him at the end of the year, but I'll speak to the owners."