The application, for Ote Hall Farm, on Janes Lane, was given the nod by the planning committee on Thursday (January 13).
Permission for a larger scheme was given last January but the meeting was told that the rising cost of building materials had led to it being reduced in size.
Owned by the Godman family since 1530, the farm specialises in rearing pure Sussex cattle and also houses a business park in its old dairy buildings.
Carola Godman Irvine said the tea room would be known as The Country Kitchen and she hoped it and the shop would be up and running by the autumn.
She said: “This project is increasingly important for the future of Great Ote Hall and Ote Hall Farm.
“The financial future of small family farms is increasingly uncertain.
“Although we have had to reduce the size of the overall building due to financial constraints and inflated build costs, this will not impact upon the look of the building.
“Smaller is still beautiful.”
A planning statement submitted with the application said 20 full-time jobs were expected to be created.
On top of that, a Godman Foundation would be set up to promote the education, training and mentoring of young people, including those with learning difficulties.
This would be achieved by setting aside a percentage of the profits from the business.
There will be parking for 74 cars and secure cycle parking for 20 bikes.
The application was given unanimous approval by the committee.
To view the plans in full, log on to pa.midsussex.gov.uk and search for DM/21/3607.