The champion jockey went into Tuesday's racing by winning the second race, the Hampton Magna Novices' Chase, on Shampooed.
He then climbed aboard Shepherds Rest, the 5/1 joint second-favorite, in the three mile, 110-yard (5 kilometer) Barford Handicap Chase.
Always keeping up with the leading pack on the 10-year-old, he kicked on and quickly moved six lengths clear. McCoy was able to ease his mount down as he crossed the line to record his 269th winner.
McCoy went into the next race, the two mile (3.2 kilometer) Leek Wooton Novices Handicap Hurdle on Valfonic, which been backed down from 10/1 to 4/1 favorite and steered the 4-year-old to victory out of a field of 21.
Valfonic appeared to be struggling but McCoy produced a late burst from the gelding to charge through and post his 270th winner.
"Obviously it's brilliant to get there in the end," said McCoy who placed third on 2/1 shot Sure Touch in the final race of the day. "It's taken a while as I keep saying I can't make the horses go any faster as much as I'd like to be able to but I can't.
"I actually thought I would struggle today as I thought Shampooed, Shepherds Rest and this one just had chances and I'm obviously really pleased that all three have won."
Trainer Martin Pipe, who has provided most of McCoy's winners this season, was delighted the jockey had reached the landmark on one of his thoroughbreds.
"It's absolutely brilliant that he should beat Sir Gordon Richards' record and I'm thrilled to bits for him," Pipe said.
"I'm highly delighted he was on one of my horses. He deserves it, he's a dedicated, brilliant jockey. He's a fabulous, generous team player."
John Francome, a former champion jockey who is now a TV racing pundit, saluted McCoy's triumph.
"I'm sure that will be a relief for him!" Francome said. "I'm absolutely delighted for him.
"I know (flat racing jockey) Frankie Dettori tried to equal the record a few years ago but got absolutely exhausted doing it. Fifty-five years is a long time for any record to stand. I knew Sir Gordon Richards well and he would have been thrilled."