The family-run company is reportedly investing £1.5m to refurbish the grade II listed Lawn complex.
It will reopen as a café, theatre, coffee roastery and barista training centre running accredited courses for hotels and restaurants throughout the UK.
The engineering department will have a dedicated workshop and training area, specialising in traditional espresso machines as well as other hot drink making equipment.
Nick Peel, managing director of Stokes, said: “We are absolutely thrilled to have completed on the purchase of The Lawn. It is so exciting to think about what lies ahead of us and we are looking forward to the challenges of taking on another iconic building in Lincoln.”
Stokes was founded in 1902 and is currently run by the fourth generation of family members.
The company - which also owns two restaurants in Lincoln - is set to relocate its wholesale business to The Lawn as it has outgrown its existing production capacity.
The Lawn was built in the early nineteenth century and provided psychiatric care until it was closed by the NHS in 1985.
It was bought by Lincoln city council in 1986 and saw the construction of a children’s play area, concert and banqueting hall, museum, tropical garden and a small theatre.
The local authority handed the keys to Stokes on 1 August following a two-year planning process.
Stokes said they were keen to see space within the site used by other businesses and had already been approached with some ‘interesting propositions’.