Doyle, 23, set a new best score for the number of winners ridden by a female rider in 2019 with 116 successes and last month rode her first Royal Ascot winner on Scarlet Dragon.
She is sitting fifth in the jockeys' championship with 38 wins and has 72 victories altogether to her name in 2020.
Al Sagar has also owned G1 winners Decorated Knight and Araafa with Saleh Al Homeizi and has 30 horses in training, spread among a number of trainers including John Gosden, Roger Varian and Roger Charlton.
He said: "We are thrilled to add Hollie Doyle to our team. We have all been impressed with how Hollie has risen to become one of the best of her profession. She is an extremely dedicated, strong and astute jockey.
"We have some lovely horses to run for us this season and I look forward to Hollie becoming an invaluable member of our team."
Al Sagar has enjoyed more than 40 stakes race winners. In addition to Authorized, Araafa won the Irish 2,000 Guineas and Decorated Knight the Irish Champion Stakes. The owner stands 45 mares at Blue Diamond Stud in Newmarket.
Doyle said: "I am delighted to be teaming up with Imad Al Sagar for the near future. I hope that we will have plenty of success."