The 26-year-old joins from National League South neighbours Oxford City, for whom he appeared thirty times last season after signing from Hemel Hempstead Town in the summer of 2015.
Walker has experience playing in the National League with Kettering Town and has good pedigree, having also seen service with MK Dons, Cambridge United and Morecambe.
A commanding keeper and a great communicator, he had a brief spell at St James`s Park in 2012/13 before moving to Hemel.