Brown attended Caterham School in Surrey, where he won the Cricket Society's Wetherall Award for the most promising all rounder in school cricket in 1986, and his early promise led to second XI games for Surrey in 1988. He made his first-class debut in 1992 and was awarded his County Cap in 1994. He shared the Walter Lawrence trophy (with Carl Hooper) in 1998 for scoring the season's fastest first-class century in just 72 balls against Northamptonshire at the Oval including 10 fours and 6 sixes.

Brown scored 268 against Glamorgan at the Oval in the 4th round of the 2002 Cheltenham & Gloucester Trophy, a world record individual high score in all one-day cricket. His innings took 160 balls and included 30 fours and 12 sixes. Surrey's final total of 438 – 5 in 50 overs was almost matched by Glamorgan who scored 429 all out and is remembered as the highest scoring one day match in the history of county cricket. Brown's innings broke Graeme Pollock's 27-year-old record of 222. His partnership of 286 with Ian Ward was the Surrey record for any wicket in one day cricket until broken by the 294 added by Brown this time with James Benning in 2007 against Gloucestershire in which Brown scored 176 off just 97 balls. The '268 Bar' at the Oval cricket ground is named after Brown's innings.

Alistair Brown mostly opened for Surrey in one day cricket, as opposed to his usual Championship batting position of number 5. He holds the record for the highest score ever made in the Sunday League, amassing 203 for Surrey v Hampshire at the Woodbridge Road ground in Guildford in 1997 in a 40 overs a side match. He scored his first 100 off 56 balls, made 150 off 84 and 200 from 118 with 19 fours and 11 sixes. In the final of the inaugural Twenty/20 cup at Trent Bridge in 2003 Brown scored a match winning innings of 55* from just 34 balls in Surrey's victory over Warwickshire. In the 2004 final at Edgbaston he hit 64 from 41 balls in vain as Surrey lost to Leicestershire. He hit 30 sixes in one day cricket in 2006, second only to Cameron White.

He started the 2007 season with a century in just 50 balls against Gloucestershire at the Oval in the Friends Provident competition (50 overs a side), the 7th quickest century in English one day cricket and the 12th fastest of all time. He set a new record partnership of 294, in less than 34 overs, for any wicket in one day cricket for Surrey with James Benning, beating his own record of 289 with Ian Ward. He passed 150 runs in just 81 balls and scored 176 in 97 balls, with 8 sixes and 20 fours before missing a reverse sweep. The scorer of 19 one day centuries, he is one of the few contemporary English batsmen to have scored 10,000 runs in list A one-day cricket.

Up to the start of the 2008 English season Brown had scored 14,705 runs in first-class cricket at an average of 43.50 with 44 centuries and a highest score of 295 not out against Leicestershire at Oakham School in 2000. Ali Brown has taken 2 first-class wickets with his off spin, taken 236 catches, mostly at slip, and is responsible for one first-class stumping as a substitute wicket-keeper. In 2004, with a century against Lancashire, he completed the feat of scoring a first-class century against every other English county.

He played in the Surrey team that won