Fox has been director of group comms at technology firm Smiths Group since 2005.
Prior to this, he was director of corporate relations with food manufacturer Tate & Lyle for six years. He starts his new role early next year.
Meanwhile leader Nick Clegg's spokesperson and director of media Hannah Gardiner left her role last month. She was replaced by head of media Lena Pietsch.
The party has been on the hunt to replace Jonny Oates since he announced last June that he was returning to his former employer Bell Pottinger after 15 months in the role.
Oates left the party at the end of the conference season and took up his new strategic media director post in October.