Born in Edinburgh, McWilliam was educated at St George's School for Girls[1] in the city and Girton College, Cambridge, where she obtained first class honours.
[6] In early 2006, McWilliam began to experience the effects of blepharospasm and became severely visually impaired as a result.
[7] In 2009 she underwent an operation which harvested tendons from her leg in order to suspend her eyelids open, thus curing her blindness.
In an article in The Sunday Times, McWilliam described her two years of blindness and the pioneering surgery that restored her sight.
[8] McWilliam's first marriage to Quentin Wallop, 10th Earl of Portsmouth, produced a daughter and a son, Viscount Lymington, but ended in divorce.