Born in St. Helens, Brown played junior rugby for several teams, including Thatto Heath Crusaders, Haydock Warriors, Pilkington Recs and Blackbrook. Although he initially struggled to impress scouts, he was signed by Wigan Warriors at the age of 16. Brown played for Wigan's academy side in 2002 and 2003. Brown was called up into the 2002 England Academy squad that beat the Australian Schoolboys in winter 2002. He had originally been included in the stand-by squad, but got his chance following the failure of Hull centre Kirk Yeaman to recover from a shoulder injury. Brown was also selected for the Super League U21s squad to face the National League U21s in June 2003. Shortly afterwards, Wigan acknowledged the player's tremendous potential by extending his contract until the end of 2005. Wigan coach Stuart Raper commented: "I am delighted Kevin has re-signed as he is a big part of my future plans."
Wigan Warriors
In April 2003, due to a significant number of first team injuries, Brown was one of several academy players to make their senior début against his hometown team St. Helens, appearing as a substitute in a 24–22 victory over the St. Helens. He scored his first tries later in the season with a hat-trick against Halifax. Brown became a first team regular during the 2004's Super League IX, playing almost every game until he fractured his fibula in a match against the Wakefield Trinity Wildcats. Despite injury and shaky form, he signed a new deal in July 2005 keeping him at the Wigan Warriors until the end of the 2007's Super League XII. Newly appointed head coachIan Millward commented: "Kevin is still only 20 and a very exciting player. He is still improving and as he gets better, which I am sure he will, he will be an important part of our attack."
Huddersfield Giants
In June 2006, Brown joined Huddersfield Giants on loan until the end of the season. On 19 August 2006, Brown made the deal permanent, signing a three-year contract with the club. In 2009, Brown signed a new three-year contract, keeping him at the club until 2012.
In May 2012, it was announced that Brown had signed a four-year contract with Widnes from the 2013 season for an undisclosed fee. He was named at stand-off in the 2014 Super League Dream Team, and was the first ever Widnes player to be selected in the team. Brown was also named as captain for the 2015 season following the retirement of previous captain Jon Clarke.
In June 2007 Brown was called up to the Great Britain squad for the Test match against France. He was selected to play for England against France in the one-off test in 2010. He was also a part of England's Four Nations campaign later in the year. In October 2016, Brown was selected in the England squad for the 2016 Four Nations. He returned to the international scene where he featured in a test match against France, scoring his first international try in the process, in his country's 40-6 win. Brown was a surprise inclusion in England's 2017 World Cup squad. He was not selected for the first two group games, with Gareth Widdop and Luke Gale being preferred as the starting halfbacks. Brown has given his first start in the final group game against France, with Widdop moving to the position. He retained his place for the 36–6 quarter final victory over Papua New Guinea, but was substituted at half time after suffering a concussion. He was cleared to play in time for the semi final against Tonga, helping England win 20–18 to reach the World Cup finalfor the first time in 22 years. Brown started once again at stand off in the final against Australia, which England went on to lose 0–6.
