Phil Reed, one of the managing partners at Leeds-based Brass, has decided to leave the business after 10 years.
During his time at Brass – which used to be known as Brahm – he headed the agency’s public relations arm.
He also recently took on responsibility for new business opportunities.
John Morgan, the agency’s chief executive, said: “Phil has made an enormous contribution to the agency over the years, we are extremely sorry to see him go and he will be missed.
“We wish him all the best for the future and we know that whatever he chooses to do will be a great success.”
Mr Reed said: “I’ve hugely enjoyed my time working in a great agency full of really talented people, and it is a massive wrench to leave.”
He added: “I haven’t made any decisions about the future, but after 10 years I’m looking forward to a fresh challenge and whatever direction it takes I hope it is as rewarding as my time at Brass has been.”
Brass, which has 130 staff and a turnover of around £16m, was founded as Brahm 28 years ago.
Last year, Brahm and its digital arm, swamp, decided to rebrand as Brass.
The company said digital marketing would sit at the centre of its business.
Its client range includes Government departments, large corporates and small and medium-sized businesses.