Part of a wider masterplan for the park, which will receive £7.9m of Heritage Lottery Funding, the single-storey café will 'relate to Chiswick House while being clearly separate from it'.
A colonnade of stone pillars will span across the café's main elevations, providing an arcaded area around its perimeter.
The building's interior will be 'extensively glazed' and will provide seating for 80 people, while the covered external space will seat a further 40 - all with views over the surrounding gardens. A forecourt will offer further seating.
Practice partner Peter St John said: 'Chiswick House and its gardens were the site of extraordinary innovations in architecture and landscape design and we are conscious that to build even a small building here is a responsibility.
'Our design refers to the white stone pavilions that mark out the different spaces of the park, and the new building will be a catalyst for the revitalisation of the garden areas around it.'
The scheme has the full backing of English Heritage, and the proposals are expected to be submitted for planning by August.
It is hoped construction will begin in summer 2008 with completion set for autumn 2009.