Mr Johnson came to the constituency to campaign with Ryan Stephenson, the Conservative candidate in next month's Batley and Spen by-election.
Voters are set to go to the polls to choose their new MP on July 1.
Mr Johnson described his visit to Fox’s as a “personal pilgrimage” because his long-time PA, Ann Sindall used to work there.
Asked about his favourite biscuit, he replied: “My favourite biscuit I had today was a Fox’s jam and cream I think it’s called. It was terrific."
Rob Beeston, managing director of Fox’s Biscuits, said: “We were delighted to host the Prime Minister, Boris Johnson, at the home of Fox’s Biscuits and showcase the passion and the people behind our products.
"Since the first Fox’s biscuits were crafted in Batley in 1853, we continue to make high quality and fantastic tasting biscuits for everyone to enjoy and have a clear investment plan for growth both in the UK and worldwide.”
1. Production line
The PM and Coun Stephenson meet with staff on a visit to the Fox's Biscuits factory in Batley. Photo by Mike Simmonds
2. Manufacturing
Mr Johnson and Coun Stephenson were given a tour of the facility by staff at the factory in Batley. Photo by Mike Simmonds
3. Treats
The pair saw how some of the factory's most popular biscuits are made. Photo by Mike Simmonds
4. Campaign trail
Mr Johnson visited the factory with Coun Stephenson as part of campaigning ahead of next month's Batley and Spen by-election. Photo by Mike Simmonds