The Morocco-born winger started his career at Wydad Casablanca, before moving to America at the age of 11 to join the youth team of New York Red Bulls and ended up at the PDA Academy.
Last year Sadaoui signed with Maccabi Haifa, but due to international player restrictions was unable to make his official debut.
Ajax boss Ari Efstathiou said of Sadaoui's capture: ”Noah impressed the technical team and we are very happy to have secured his signature. He is a versatile player and the coach will be able to use him in a number of positions if called upon.”
The Urban Warriors have also secured the services of former Platinum Stars defender James Mofokeng on a two-year contract.
Coach Roger de Sa has also promoted attacking midfielder Ziyaad Eksteen to the first team from the development ranks, and Efstathiou is confident the 18-year-old will make his mark at senior level.
“Once again the Ajax Youth Academy has proved its value. This fine youngster has been in the academy since the age of ten and impressed the technical team on many occasions. I am convinced he will become one of our future stars within the first team,” said Efstathiou.