Born in Chelmsford, Eales moved to Newcastle in July 2022 from Major League Soccer club Atlanta United, where he served as the President and Chief Executive from when the team was founded in 2014.
During his time at St James' Park, Newcastle reached its first domestic cup final in 24 years, losing the League Cup final to Manchester United in 2023, and also returned to the Champions League last season.
"Being CEO of Newcastle United is an extraordinary privilege and I am incredibly proud to be part of the club's exciting journey," Eales said in a statement.
"However, it has become apparent to me that now is the right time to make this decision so that I can prioritise my health and my family.
"In the short term, it will be business as usual in terms of running the club's day-to-day operations, and I will give my full support to a transitionary period that will enable the board to carefully assess and appoint my successor.
"I'm proud of what we have collectively achieved and I'm excited to see what's ahead for everyone as the club builds towards a future of sustained success."
Eales will continue to lead the club's executive team until a successor is appointed, Newcastle said.
