They will start on April 7th at St Jean Pied de Port (the traditional starting point) and finish by June 7, 2017 at the Church of St. James of Compostela.
The distance is 750.5 kilometers/488 miles.
Mark and Nancy are doing this to raise money for The Nestling Trust, the charity co-founded by their friend of many years, Sue Hamblin.
The main project of the Nestling Trust is to build a group home (not an orphanage) for 20 children in Sarangkot, Nepal.
This home is going to provide protection and hope to destitute and abused children in a country where human trafficking is rife.
Just $5 (£4.00) would be enough to buy 1 blanket for a child's bed.
Mark and Nancy hope to raise £1000.