A middle-order batsman, Walsh made his first-class debut for Oxford University in 1966, scoring 56 against Hampshire in his second match,[3] but was unable to maintain his form and lost his place in the side.
He struggled again in 1967, but kept his place in a weak side, and "fought his way doggedly out of his past to achieve reliability".
In the third match in 1969 he "produced a variety of strokes hitherto unseen from him"[7] when he scored 207 against Warwickshire, with 32 fours and two sixes, adding 270 for the sixth wicket with Stuart Westley.
He played seven matches between 1966 and 1972 for Sussex Second XI,[10] but all his first-class cricket was for Oxford University.
A Duty to Serve: Tonbridge School and the 1939-45 War was published by Third Millennium in 2011; Public Schools and the Great War: The Generation Lost, co-written with Sir Anthony Seldon, was published in 2013 by Pen & Sword; Public Schools and the Second World War, again co-authored with Sir Anthony Seldon, was published by Pen & Sword in August 2020.