BJL was selected to create an above-the-line campaign to promote the Free From range, which includes white and brown loaves, teacakes, sub-rolls and muffins.
Warburtons' relationship with WCRS, which picked up the baker's main £8 million account in July, is not affected by BJL's appointment.
It is understood that BJL beat two undisclosed agencies in the final stages of the process. The media planning and buying for the campaign will be handled by Mindshare.
Warburtons believes that Free From's retail and prescription markets both have significant growth potential because of the rising awareness and diagnoses of gluten-sensitive conditions.
Chris Hook, the Free From director at Warburtons, said: "We are looking forward to seeing the fruits of BJL's strategic and creative excellence."Follow @MaisieMcCabe