Gordon Moulsdale, who has been head of Bishopbriggs Academy since 2006, will leave the school next month.
He broke the news to parents in an online message.
He said: “I wanted to take this opportunity to inform you with an extremely heavy heart that I will be leaving Bishopbriggs Academy at the October holiday.
"Although I’m leaving the school, I don’t feel quite ready to retire just yet and I have decided to take up the offer of a senior position within my brother’s company.”
He added: “It has been by some distance the biggest honour and privilege of my professional life to be Head Teacher of this wonderful school.
"Over my almost 16 years at the school, I have had the great pleasure of working with countless numbers of incredible young people and many outstanding colleagues.
"I believe that the quality of experience on offer in this school is the envy of many, many people throughout the country. I am extremely proud of our achievements and the reputation that the school enjoys.”
He said: “Obviously the past 18 months have presented many challenges for everyone, both personally and professionally.
"I know of no other group of staff, past or present, who are so willing to give of their time to ensure pupils are given the chance to shine.
"I’ve also had tremendous support from parents, carers and extended families over the years.
"There are no words to adequately describe how much this has meant to me. I can assure you it is something I will never forget.
"By any measure, Bishopbriggs Academy is a truly outstanding school and I know it will continue to go from strength to strength in the coming years.
"I will always cherish the time I have spent here.”
Bishopbriggs councillor, Gary Pews, thanked Mr Moulsdale for his years of service.Councillor Pews said: ''Gordon Moulsdale's inspirational leadership has seen Bishopbriggs Academy become one of the top state schools in Scotland.
"I have met Gordon on many occasions over the years and each time he simply radiates with pride in the achievements of his students, both academically and personally.
"Gordon's departure is a blow to the school and whoever takes over will have big shoes to fill, but he leaves a very solid foundation upon which his successor can build.
"I thank Gordon for his outstanding service to Bishopbriggs Academy and wish him well in his next venture''
East Dunbartonshire Council has said the recruitment process for the new Head Teacher post is presently underway.