Lynch previously spent seven years with banking firm Santander as HR director, and has substantial experience gained in the retail sector with Sainsbury's and Tesco.
Her experience spans the HR spectrum, from influencing and leading organisational change, coaching and talent development through to HR services.
Lynch will report to group chief operating officer, Matthew Donaldson.
Donaldson says: "Our continuing growth is dependent on our strategic objective to attract and retain exceptional people. Catherine's expertise and innovative approach across all areas of HR will be invaluable in helping the group achieve its ambitious plans for further growth and ongoing success."