Warner became Liverpool reserve 'keeper in 1994/95 when Stensgaard got injured. The Liverpudlian was 120 times on the bench for Liverpool, but never got to play for the first team. He was released in 1999 and went on to play 225 games for Millwall. Warner got his big break in the top-flight with Fulham in the 2005/06 season and later that season made his international debut for Trinidad & Tobago. Whilst on Fulham's books, Warner also had loan spells at Leeds, Norwich and Barnsley. On 16 July 2008 Warner moved to Premier League newcomers Hull City. After a brief loan spell at Leicester City, Warner left Hull by mutual consent and had brief spells at Charlton Athletic, Leeds and Scunthorpe United. Warner signed for Tranmere Rovers on 6 January 2011 and made 25 League One appearances until the end of the 2010/11 season, passing his thirty-seventh birthday. The latter-day John Burridge joined New Zealand's Wellington Phoenix in the summer of 2011.

Still active in his thirty-ninth year, Warner joined Maltese club Floriana in October 2012 and made twenty-six first-team appearances for them between October 2012 and May 2013.

Warner returned to England in the summer of 2013 to became a member of Blackpool's coaching staff. Although he had not played in an English Football League match since being with Tranmere Rovers in the 2010/11 season, the goalkeeper was an unused substitute when Blackpool met their Lancashire neighbours Bolton Wanderers at Bloomfield Road early in October 2013. At the end of the season he left and began coaching with Bolton wanderers, but signed as emergency cover for Accrington Stanley in March 2015. He was released at the end of the season and looked set to join North East United in the Indian Super League but the club terminated his contract due to him also having a role at Bolton. As of September 2016 he is the academy goalkeeper coach at Bolton and pundit for Wirral Radio.