King, previously sales and marketing director at Orchard House Foods, will take over from Robert Gilham, who becomes chairman.
Co-founder Harry Cragoe has responsibility for the firm's business development.
The appointment heralds a renewed focus on marketing, which in June saw St Luke's hired to handle the £2m advertising account for the soft drinks firm. Creative development was previously handled in-house.
PJ plans to boost marketing to promote its range of smoothies. It will hire its first marketing director next month. It claims to be market leader in the UK smoothie sector, with 41% value share.