Cornwallis was serving under
Field Marshal Haig when he played in a charity cricket match, taking a
hat-trick. He was later invited by
C. H. B. Marsham to play for
Kent County Cricket Club against
Sussex in the
1919 County Championship. Cornwallis, who had not played cricket since school, initially laughed off the invitation but was told by Haig to accept – being told it was "one of those things you have got to say you have done once, Cornie". He took a wicket in the match and went on to play several more times for Kent in 1919. He was
capped by Kent in 1923 and captained the team after his retirement from the Army between 1924 and 1926, playing much more regularly during this period. During his three years as Kent captain he was only able to bowl 560 overs, although his leadership abilities were strong enough to see the county to top-five finishes in the
County Championship in each season. He was also considered a "good field" although "not normally regarded as a batsman". His highest score of 91, his only half-century, was made against
Essex at
Canterbury in 1926. This was his final year as captain and his last playing first-class cricket. He remained associated with Kent and was President of both the county club and
MCC in 1948. ==Honours==