Brooke (pictured) will leave the broadcaster in early 2019 to launch a marketing and communications business. His new company will focus on "helping companies be mission and purpose-driven".
He said: "I’m proud of the things my incredibly talented marketing and communications teams have achieved and that the most groundbreaking of this work has achieved such powerful results and consistent global recognition.
"I’m also proud to have been the board champion for diversity and inclusion, leading the drive that saw Channel 4 voted Britain’s Best Diverse Company.
"With the '4 All The UK' plan now successfully launched, it’s a good time to leave on a high and use these successes as a springboard for my burgeoning ambition to help other mission and purpose-driven companies grow."
Channel 4 said the next steps following Brooke’s departure will be announced in due course.
The press and publicity team, which includes corporate communications and the programme/content PR team, will continue to be led by head of press & publicity James MacLeod. Sophie Jones will stay as head of corporate relations.
Brooke joined Channel 4 for the second time in 2010 in the newly created position of director of marketing and communciations, reporting directly to then chief executive David Abraham, who had joined a few months earlier. Jay Hunt, the chief creative officer whom Abraham had hired shortly before Brooke in 2010, left Channel 4 last year to join Apple.
Between 1998 and 2005, Brooke was head of marketing and development for Film4, before rising to managing director of digital channels.
During his time away from Channel 4, he was managing director of indie production company Rare Day for a year, following four years as managing director at Discovery Networks UK.
Alex Mahon, Channel 4's chief executive, said of Brooke: "Dan has made a huge and far-reaching contribution to the life and success of Channel 4 over many years. I’d like to thank Dan personally for the support and advice he has offered me in my first year and, on behalf of the whole organisation, wish him the very best with his future plans."
This article was updated by PRWeek with information about the comms operation