In 1968, McKenzie became a full-time cricketer, believing that it would offer him the best chance of financial security. At the time the Australian Cricket Board regarded its players as amateurs and paid them accordingly. McKenzie joined Leicestershire, captained until 1968 by the Western Australian skipper and former England Test stalwart Tony Lock. He took over four hundred wickets for the county and was instrumental in its four One Day Cricket trophies in the early 1970s and winning their first County Championship in 1975.