The company has handed retained press office work to Consolidated PR and shared its campaign work between Hope&Glory and Margaret.
PRWeek revealed Sony's plans to divide the brief held by Cake for the past two years in June.
Cake’s social media and experiential work, which it won in the same year as picking up the wider PR brief, is unaffected.
Sony's electronics division includes a wide range of devices, such as Bravia televisions, Cyber-shot digital cameras and Vaio laptops. It has struggled at a global level and has been unprofitable for the past two years.
A Sony UK spokeswoman said: ‘All three selected agencies impressed us with their enthusiasm, creativity and tenacity, and we look forward to working with them.’
Marlin PR continues to be retained by Sony’s professional solutions business in the UK.