His appointment coincides with the independent agency's brand refresh, revamping its approach to one of collaboration between colleagues, clients and creative partners.
"Robert brings something very unique to our business. He has been on our journey. A founder at Fallon London, he has grown an agency into a global powerhouse before leading one of the world's most famous agency networks - Saatchi & Saatchi," Patrick Meade, partner and managing director, Boys and Girls said.
Senior's career in advertising has spanned 30 years. In 1998, he founded Fallon London with four partners and together they grew the business to a multi award-winning agency, which was named Campaign's Agency of the Year in 2006 and 2007.
The partners sold Fallon London to the Publicis Groupe in 2006, prompting Senior’s move to its sibling agency Saatchi & Saatchi where he held positions as UK chief executive, chief executive of EMEA and Worldwide chief executive.
Senior (pictured above), stepped down as global chief executive of Saatch & Saatchi last year.
Commenting on his decision to join Boys and Girls, Senior said: "I was instantly drawn to their passion, creativity and independent spirit."