The changes result in the Publicis-owned Fallon joining the Nestle stable of agencies with worldwide work on a number of key brands being produced out of its headquarters in Minneapolis.
Bates and Lowe have been dropped from the petcare roster, while DDB Worldwide and the McCann-Erickson subsidiary Avrett Free & Ginsberg will also benefit from extra assignments for North America, Japan and Latin America.
The realignment, which has been under discussion for the past six months, comes after Nestle's £6.7 billion takeover of the US-based manufacturer Ralston Purina at the beginning of last year.
The merged division (called Nestle Purina), which brings brands such as Nestle's Friskies and Ralston's Dog Chow under one umbrella, is in line with Nestle's ambition to rival Mars, which makes Whiskas and Pedigree, in the petfood stakes.
The Publicis group emerged as a significant winner in the shake-up, building on a relationship with Nestle that stretches back to the beginning of the 50s.
Fallon, which had previously handled a small amount of Ralston's business, will co-ordinate worldwide advertising for the Dog Chow, Puppy Chow, Pro Plan and One brands.
Maurice Levy, the Publicis group chairman, said: "We have provided a tailor-made solution for Nestle that takes advantage of Fallon's existing expertise in the petcare market and the strength of the Publicis worldwide network."
DDB Worldwide expects to increase its pan-European billings by about £25 million - including £2.5 million in the UK - with its appointment to handle the Felix, Gourmet, Bakers Complete Dog Food, Friskies, Cat Chow and Kitten Chow brands.
Nestle's ambition is to be a world leader in petfood. The Swiss company estimates it is a global market worth $38 billion. It believes the sector offers serious growth opportunities in a consumer goods business that offers few obvious areas for expansion.