Norman arrives with experience and a proven record, having taken compatriot Robin Soderling to the top five in the rankings and two French Open finals before guiding Swiss Stan Wawrinka to three Grand Slam titles.
The 50-year-old Swede will take his place alongside coach Simone Vagnozzi, who like Cahill started working with Italian Sinner in 2022.
"A large part of who I am, as a player and as a person, I owe to you," Sinner said about Cahill in a video posted on Instagram.
"Of these five seasons, I won’t forget a single day. Thank you, my friend, for everything. It has been a privilege."
Sinner has been out of action with a persistent knee injury since capturing the fifth Grand Slam title of his career at this year's Wimbledon in July, but is expected to make his comeback in December at the Six Kings Slam exhibition in Saudi Arabia.
Cahill, a veteran coach who has guided four players to the world number one spot, was expected to leave Sinner's team in 2025 but stayed on for another year and said at Wimbledon he would stay until the end of 2026 before discussing his future.
Sinner went from a rising talent to the tennis summit under Cahill, although his ascent was interrupted by a three-month ban in 2025 after two positive tests for trace amounts of clostebol in 2024, for which he was cleared of wrongdoing.
Alexander Zverev is guaranteed to finish 2026 as the year-end world number one, with Sinner deciding not to play in any of the remaining ATP tournaments this year.