McGahan, who was appointed as the right-hand man to the club's coach, Dean Bell, 18 months ago, is to become the marketing manager for Super League in New Zealand.
"It has been a tough decision for me to make, but I feel that it is a great opportunity for me to help the game in my native New Zealand," said McGahan, whose partnership with Bell failed to produce the goods during a first Super League season at Headingley.
"He will be sadly missed by everyone at Headingley, not least by myself," Bell said. "He has been a big support to me during what have been extremely difficult times and his contribution to the club should not be underestimated."
There will be no decision on how the management structure at Leeds will be re-organised until after the departure of McGahan, a former New Zealand captain, early in the New Year.
Also on the move is one of the key men at the Rugby League's headquarters, the coaching and Academy executive, John Kear.
Kear, the man who also guided Paris St-Germain away from the danger of relegation during a period on loan to them last season, is joining Sheffield Eagles as football executive.
He will link up there with Eagles' new coach, Phil Larder, with whom he has worked at international level. "I have had job offers in the past, but this one was too good to turn down," Kear said. "Phil and I are determined to take the club to the top."
The League's chief executive, Maurice Lindsay, paid tribute to Kear's work in establishing the Academy as a thriving sector within the game. A decision on Kear's successor is being delayed until the British Amateur Rugby League Association responds to proposals for unification, as this will have a major bearing on the future scope of the job.
The British and French board members of the Paris club are to meet tomorrow in an attempt to resolve the question of who will run it next season.Reuse content