Famous for playing upwardly mobile characters Margot in TV sitcom The Good Life and Audrey Fforbes-Hamilton in To The Manor Born - Miss Keith was nominated on a short-list which was passed to the Queen.
High sheriffs were historically responsible for the safety of judges within their county, and were liable for the delivery of prisoners.
Miss Keith's appointment is in keeping with a drive to recruit more women into the posts, said a Cabinet Office spokeswoman.
There are 55 high sheriffs in Britain, whose names are put forward by the existing sheriffs.
However, the posts have been criticised by the government because they are mostly held by white men from wealthy backgrounds.
Traditional appointment
Miss Keith, who will become high sheriff in 2002, is eligible for the role as she lives in Surrey.
In the next few months the actress will be slowly introduced to her duties which are mainly ceremonial although she will retain a statutory duty to collect debts and enforce writs on behalf of the courts.
Steeped in tradition, the appointment of a high sheriff starts with a nomination by the person already holding the post.
A short-list of candidates is taken to the High Court in November by the Queen's Remembrancer and the Lord Chancellor.
The following April, a scroll listing the names of the candidates is presented to the Queen, who sticks a needle next to the name of the future sheriff.