Sharecast - Scottish Mortgage said McBain, who took over as chair back in 2017, will be succeeded by senior independent director Justin Dowley.
Dowley said: "I would also like to thank Fiona for her 14 years of loyal and exceptional service to the company, in particular over the last few years (and at the request of her fellow directors) providing essential continuity, reassurance and leadership during the extraordinary circumstances of Covid-19.”
McBain's departure comes less than a week after non-executive director Amar Bhidé took aim at the trust's corporate governance, including the length of the chairwoman's tenure.
Although Bhidé's shots were still ringing out, Scottish Mortgage claims the changes to its board were the result of "succession planning" that it has developed over the last year. Bhidé has also left the board and "is no longer a director of the company", according to SMT.
As of 0855 GMT, Scottish Mortgage shares were up 0.41% at 664.89p.
Reporting by Iain Gilbert at Sharecast.com