Arnold's position had been called into doubt since it was revealed that British billionaire Sir Jim Ratcliffe was preparing to buy 25% of the club.
The owner and founder of INEOS is expected to make major changes at management level, with the jobs of football director John Murtough and director of football operations David Harrison also called into doubt.
A report earlier on Thursday said that Arnold, who has been with Man United since 2007, would leave his role as CEO, and it has now been confirmed by the 20-time English champions.
«Richard Arnold has decided to step down as Chief Executive of Manchester United after 16 years with the club,» read a statement on the English club's official website.
«Patrick Stewart will take over as interim CEO, in addition to his existing role as General Counsel, with Richard continuing to provide transitional support until the end of December. A search process will be carried out for a new permanent CEO.»
According to The Athletic, ex-Juventus chief executive Jean-Claude Blanc, who is currently working with INEOS Sport, is one of the main candidates to step into the position on a permanent basis.
Man United executive co-chairman Joel Glazer told the club's official website: «I would like to thank Richard for his outstanding service to Manchester United over the past 16 years, and wish him all the best for his future endeavours.
»We are fortunate to be able to call on the deep knowledge and experience of Patrick Stewart to provide interim stability and continuity as we embark on a search for a new permanent CEO."
Meanwhile, Arnold
Read on sportsmole.co.uk