Walker was previously hotel operations manager for the Crowne Plaza Liverpool.
Shepheard worked as a media executive at Lincolnshire Tourism.
Walker said: "I worked in my last job for six years during which time I helped to transform the hotel into an award-winning business. I felt as though my work there was done and I needed a new challenge.
"Lincoln is a bit of a hidden gem so we need to raise the profile of the city as well as the hotel. We’re here to do a job but we want to enjoy ourselves doing it and it’s about recruiting people with the right personality as well as the right skills."
Doubletree recently announced aggressive UK growth plans.