McLachlan has been with the AFL since 2000 and has been its chief operating officer since 2008, with broad responsibilities across fixturing, broadcasting, stadiums and venues and the creation of AFL Media.
He was acting chief executive officer of the AFL for several weeks last winter while Andrew Demetriou took an extended break overseas.
McLachlan will continue to perform the duties of chief operating officer in his new role.
He was a leading contender earlier this year to become the new chief executive of the National Rugby League and his decision not to see that process through to its conclusion leaves him the heavy favourite to eventually replace Demetriou.
"Gill has made a significant contribution to the AFL across a number of strategic fronts and this promotion is well deserved," Demetriou said, while announcing a restructure of the League's executive structure.
The AFL's executive team has suffered several departures in the past two months with Adrian Anderson (football), Andrew Caterall (strategy and marketing) and Christina Ogg (human resources) all moving on from the League.
The AFL has engaged an executive search firm to identify their replacements and will soon advertise nationally to fill the positions of general manager of football operations, general manager of people and culture and general manager of fan development and customer acquisition.
"It is timely to establish a new-look team at the executive level to ensure the AFL maintains an organisational structure that is aligned with our future strategic priorities," Demetriou added.
McLachlan will also be acting head of football operations from the start of next year until the permanent appointment is made to fill that position.
You can follow AFL Media senior writer Ashley Browne on Twitter @afl_hashbrowne
