Tempest-Hay has led Blue Rubicon and then Teneo for the past 15 years, during a period of rapid growth.
His chief executive responsibilities will be taken over by Teneo International chairman Charles Watson with support from Teneo’s London strategy and communications chair Fraser Hardie and the London leadership team.
Teneo vice chair Fiona Joyce has also decided to step down for personal reasons.
Tempest-Hay will focus on client work and transitioning his duties in the first six months of 2020.
He joined Blue Rubicon as its first managing director in 2004 and the rose to CEO in 2010. He continued leading the business through several transitions after it was acquired by Teneo in 2015.
Following a spate of acquisitions, Teneo amalgamated its operations of Blue Rubicon, Stockwell and Pendomer agencies in 2016 to establish its UK operation, Teneo Blue Rubicon. It continued to acquire consultancies, growing its service and geographic footprint.
A year ago, it rebranded to ‘Teneo', and has been a major disrupter in the UK communications industry during the time Tempest-Hay has been at the helm.
In an internal email seen by PRWeek, Hardie described Tempest-Hay as "without question, [he has been] one of the stand-out bosses of this generation"
"On his watch, the business has evolved from an early-stage growth business to one of the UK’s leading strategic communications consultancies at the centre of one of the world’s most successful specialist consulting firms," Hardie said.
Hardie also paid tribute to Joyce, who joined Blue Rubicon as partner after leading Porter Novelli in London.
"She has played a key role in the growth of our business since 2006 and has been instrumental in scaling up our operation, making exceptional client service a hallmark," Hardie said.
"I think it is fair to say that Fi has taught me and hundreds of others what it takes to delight clients, to manage teams in a truly client-centric way, and how to think strategically about the role culture plays in creating competitive advantage.
He added: "We will have an appropriate send-off for both, but in the meantime, I would like to thank Gordon and Fi personally, not just for their unswerving commitment to the cause, but also for their friendship and guidance over the years."