Helm most recently launched snack food company Bear with former Innocent commercial director Giles Brook. He will now leave the company but will continue to be a non-executive director.
He replaces Fiona Hughes at Mars, who was promoted to the newly created role of global petcare marketing director for its cat brands.
Helm will oversee Mars brands including Pedigree, Cesar dog food, Sheba cat food and Whiskas.
He left Innocent last year to set up his own marketing consultancy after just over one year in the role.
Prior to joining Innocent, Helm was a Nestle brands controller for its Cereal Partners business. He was responsible for driving the health agenda for brands such as Shredded Wheat, Cheerios and Shreddies.
Mars recently signed a five-year agreement with the Football Association to become an official “supporter” of the English national team as well as an official supplier.