The move, which will see Clarke work in the UK for the first time, follows the departure of Kevin Dundas, the president and chief executive of SapientNitro, who left to join 180 Amsterdam earlier this month.
He was appointed in January shortly before Nitro was acquired by Sapient in a deal worth $50 million (£30.76 million).
Clarke will oversee the integration of SapientNitro, and Sapient Interactive, which will be brought together under one roof.
Their offerings will remain separate with SapientNitro handling brand planning and digital creative briefs while Sapient Interactive will continue to handle pure-play digital build accounts.
The agency is close to appointing a group executive creative director to oversee the creative output across both units.
A shortlist of candidates has also been drawn up for the managing director position, which has remained vacant since the departure of Kate Howe earlier this year.
This article was first published on campaignlive.co.uk