Brearley was educated at the City of London School (where his father Horace, himself a first-class cricketer, was a master). While at St. John's College, Cambridge, Brearley excelled at cricket (he was then a wicketkeeper/batsman). After making 76 on first-class debut as a wicketkeeper, he played for Cambridge University between 1961 and 1968 (captaining the side from 1964 onwards), first as an undergraduate in the Classical and Moral Sciences tripos, and then as a postgraduate.

While still at Cambridge he was chosen for the Marylebone Cricket Club (MCC) tour to South Africa in 1964–65, and to captain the MCC Under-25 side in Pakistan in 1966–67, when he scored 312 not out against North Zone (his highest first-class score) and 223 against the Pakistan Under-25 side he ended the tour with 793 runs from six matches at an average of 132.

From 1961 onwards, he played for Middlesex County Cricket Club, often opening the innings with Michael Smith. As captain between 1971 and 1982, he led Middlesex to County Championships in 1976, 1977 (jointly with Kent), 1980 and 1982; and he appeared in Free Foresters' very last first-class fixture, in 1968, keeping wicket and scoring 91.

In part because of his pursuit of an academic career as a lecturer in philosophy at the University of Newcastle-upon-Tyne, which limited his cricketing activity in 1969 and 1970, Brearley was not selected for England until the age of 34 in 1976. His record in Test cricket as a batsman was mediocre (he averaged 22.88 in 66 Test innings, without a century), but he was an outstanding captain. Having previously kept wicket, he was also a fine slip catcher, usually at first slip. He took over as captain of England in 1977.

His management skills (he was once described by Rodney Hogg as having "a degree in people") drew the best from the players in his team, although he was fortunate to be able to call on the services of Bob Willis, David Gower and Ian Botham at their peak. Brearley was captain during the infamous aluminium bat incident in 1979, when he objected to Dennis Lillee's use of the bat, instead of one made of willow. On the same tour he caused controversy by ordering all his fielders including the wicketkeeper to the boundary with three runs required off the last ball of the match (this was legal by the rules of the time).

He had been an innovator regarding cricket equipment himself, wearing a 'skull cap' under his England cap in 1977. It consisted of a plastic protector with two side pieces protecting his temples. It was later popularised by the Indian batsman Sunil Gavaskar.

Brearley captained England to the fin