Simon's new role will be executive head chef and manager.
He said: "It's something I've done before and look forward to developing a bit more and also to take the pressure off Jane and David."
Jane said: "Simon's worked in some fantastic hotels. We're not a big hotel so there's not going to be anything happening here that surprises him."
She said they would like to develop the hall, which is currently known for its small weddings, conferences and family occasions, to include a "more contemporary offer".
The dining room, drawing room, and lobby area are all currently being refurbished and will re-open on September 15.
There will be two menu styles for diners to choose from - one with a fine dining option, and another with more informal, classic dishes.
There will also be a wide range of drinks and cocktails and there are plans to start serving Sunday lunch from November.
Simon said: "Speaking to Jane and David about the hopes and visions for the restaurant - it's exactly the same direction that I would want to take Moresby Hall in."
Jane said they were keen to let Simon put his own stamp on the restaurant but he has stressed that he will not be re-creating The Waterfront.
He said: "It's a new entity. It's a new journey we're all embarking on."
The De Millom restaurant can seat up to 32 people and an additional 14 can be accommodated in a private dining area, which is suited for corporate dining and family occasions.
"The intention for us isn't to rush guests out it's for them to be able to be here and relax and enjoy the ambience," Jane added.
To keep up to date with Moresby Hall, visit www.moresbyhall.co.uk or search for Moresby Hall on Facebook.