Smythe confirmed both founders will leave at the end of next month, taking five months’ gardening leave.
He said the merger sparked off their decision to quit: ‘I’ve been around for 14 years since SDL started up and the two business are going to merge, so it seemed like a good time.’
The newly merged entity will be led by Interbrand chairman Rita Clifton, with SDL director Ian Buckingham appointed MD of the internal communications division.
Clifton said merger details were still being thrashed out and it is unclear whether the SDL brand will remain.
She added that redundancies were a possibility.
Omnicom aims to create a new offering within Interbrand through the merger, focusing on company culture rather than visual branding.
Interbrand is the larger of the two agencies, with 150 staff in the UK compared with SDL’s 22.