An announcement by the firm today revealed Mr Holmes will relinquish his role on November 30, after 22 years at the firm.
He will leave the company at the end of the year.
The UK investment management business will be co-led by head of London Robin Eggar and head of regions John Wallace after Mr Holmes has stepped down.
They will report to chief executive Caroline Connellan, who joined from HSBC last year.
the firm paid tribute to Mr Holmes in a statement which read: “Nick has played a critical role in Brooks Macdonald's growth and success over the last two decades and has been a valued member of the leadership team.”
Brooks Macdonald chairman Chris Knight said: “I would like to thank Nick, whose contribution from the firm's early days and in particular his leadership of our UK investment management business since 2008 have been major factors in our success to date.
“His commitment, leadership and passion for Brooks Macdonald have significantly helped shape the business we are today.”