The 19-year-old, who is based with John and Thady Gosden, has been neck and neck with fellow rider Harry Davies throughout the course of the season.
The 17-year-old Davies who is based with Andrew Balding, ensured the title race was a close-run thing, but De La Sayette's efforts have left him unbeatable with the championship race ending on Qipco British Champions Day.
Currently tallying 61 winners for the campaign, De La Sayette is six ahead of Davies and sealed matters when riding a winner at Chelmsford on Thursday evening.
Previously De La Sayette landed a valuable handicap when winning Ascot's Victoria Cup aboard Kevin Philippart De Foy's Vafortino, with a three-timer at Wolverhampton and big-meeting success at both Glorious Goodwood and the July Cup fixture among the highlights of his season.
"I am thrilled to win the champion apprentice title. It's felt like such an amazing season and I've really enjoyed the battle with Harry," he told Great British Racing.
"I wish him all the very best for the future and hope we're riding against each other for many years to come.
"There have been plenty of highlights, starting with Vafortino winning the Victoria Cup at Ascot in May. I was also lucky enough to ride a winner at the July Festival (Adjuvant) and have victories at Glorious Goodwood (Trawlerman and Caius Chorister).
"At the start of this month I rode my first-ever three-timer and that was another day I'll never forget.
"None of those moments - or the other winners I've had - would have been possible without the fantastic support I've received from so many owners and trainers throughout the year. I'm especially grateful to John and Thady Gosden, as well as the whole Clarehaven team. I have learnt so much from the amazing team there.
"The input and advice from my agent Paul Clarke has been so valuable as well. He has worked tirelessly to get me opportunities. I'd also like to thank the PJA (Professional Jockeys' Association) for all their ongoing support.
"Last but not least is my family. I want to say a big thank-you to all of them, especially my mum and dad for everything they do - this one's for them."